I know a few of companies paying easily $80k to $100k / year for great interns... You need also to look at cost of life in the area...
With all that text about what you want and how things should operate, I do not see any mention of resetting the system back to an original starting position. Why?
Thank you 
Because this is an overview, not specs.
OK, first let me say that I am sorry if I somehow opened a can of worms. I didn't expect this to be a discussion reminiscent of whether Apple or Microsoft is better 
I will try to answer some questions, and make some comments, but In the end, if you want eh TL/DR right now, the answer might be "It appears I need to spec this a lot more."
First, as to programmers making $250K - $350K... I've hired a lot of programmers. Some of them were crap. Some of them were excellent. None of them made anywhere near that, so either there's been a lot of inflation, or I got lucky. Even at my last job for a large employer, programmers were making more like $100K (this is in the US and Canada, I would think that in plenty of other places, rates are lower). So to be candid, no, $250K - $350K annualized is not even in the ballpark I was considering.
Second, this may sound stupid, but I'm doing this in my house, and have multiple projects going on at once, so just SPACE is important. Comments were made about why I was worried about spending a few more dollars on good stepper motors when the programming costs would dwarf the hardware costs. It's not all about cost. Just being small and simple has value to me because this is all sitting on a desk. Is it easier to have 10 little motors and boards, and 1 power supply split 10 ways, on my desk, or 10 larger motors, larger boards, and 10 separate power supplies?
Third, that being said, I appreciate the input of cedarlakeinstruments that I should just make 10 systems. But, not necessarily for the reason he mentioned (making it modular). Rather, I should start with 1 system, make sure it works, and replicate it from there (maybe that's just a different way of saying "Make it modular" lol). I will revise the job spec accordingly.
Fourth, if I used the word "documentation" I probably conflated "comments" and "documentation." This is a simple enough project that I am not very worried about documentation in a user manual sense. Rather, I wanted well-commented code. If an idiot can't use the UI for a project this simple without a user manual, something is wrong. So, no documentation. Again, I will revise the project description if necessary.
J-M-L, I know the motors can break the material. I've already done a bunch of testing myself, and I have the ability to simulate all of this in multi-physics programs (and just a CAD with FEA would be able to address this particular question).
rupawalaebrahim, There are no regulatory issues. There is nothing I HAVE to do in terms of following procedures, I just don't want to end up with code that is impossible to read/change/extend.
cedarlakeinstruments, I agree with you. This is not a 3 month project. Maybe this is my fault for not spec'ing it well enough, but this honestly seems like something that a skilled undergraduate could write in a few days.
If I was familiar with all the pinouts, I think I could write this in a few days. And then I'd end up picking at it, commenting it more, etc., and I'd never be happy with it (that's just the way I am), so I don't know what you'd call the total hours, but for a first cut, I'd say < 20 hours.
That may raise the question as to why am I posting this as a job at all? Simple: Because I hate C++. Maybe I should just switch to Teensy and write it in MicroPython. That may actually make sense for this project. The other one I posted, I don't know - I think it has too many pins required, which is why I wanted the huge number of pins that the Mega 2560 has (plus several ADC's).
I think that answers most of the questions, except budget. I indirectly address budget by saying I think this could be done in < 20 hours, but are those hours billed at $30/hour or $150/hr? I know which I would prefer but seriously, there is no hard number for budget as long as it's reasonable. This is not a $100K project. I am fairly certain this is not even a $10K project. But it has to get done, so if the market dictates that I am wrong, then it does. I'll either pay what I have to, or, if that's too much, I'll write it myself, probably by switching to a microprocessor that I can use Python on instead of C++.
So we are taking about 500 bucks budget?
I think it's over $500 but not more than a few thousand. Partly depends on the scope someone decides to take on (see revised description).
Summarizing the thread, along with the edits to your original post:
- Motor has user-adjustable # of max rotations
- Measure force while motor moves
- If force drops below certain threshold, stop
- Log force vs distance (distance increments TBD) in CSV format
- Logging medium TBD (SD card?)
- UI: set max distance, Start, Stop
- Attempt to keep each axis of system relatively small.
Out of scope:
- Force calibration
- Distance calibration
Does that sound more or less correct?
I'd probably do a touch-screen to set the motor parameters and start/stop, probably with an external switch as an "emergency" stop.
Yes, just one comment:
If I can log back to the computer instead of SD (or both), I'd prefer that because I've heard of a lot of SD's dying and I don't want to lose my data. If it's easy to treat the SD/arduino-clone as another drive and I can manually back up whenever I want, that's fine too.
I'm not clear on whether you are saying the HX711 is good or bad. You mention that is is very sensitive but then say "NOT precise instruments at all." Was that second part about the 28BYJ-48 stepper motors?
I think it was about a load cells.
load cells. I use mine every morning to measure coffee beans. It is permanently scaled and tared. The scale sleeps and when I wake it up the starting weight varies quite a bit but I am only measuring 28gms.