J-M-L:
I know companies that charge 500€ to 2000€ a day for mix of software and and hardware engineering work. Of course they have administrative overhead and taxAt $30 it would definitely be on the cheap side and Delat_G Is no newbie and quite experienced... - $200 does not even get you a day of work which is very far from the work needed to match specific needs of writing the code, testing and debugging
You could have a look at this Make an Autonomous "Follow Me" Cooler project - about $200 just for parts assuming you have access to a 3D printer. Not sure the wheels would go all-terrains on that one though (eg sandy beach)
There is another post where @silente offers to work for free - May be he is a good practitioner and interested in your project
I think you've rather missed the point of what I'm looking for here, but thanks for giving me a ballpark number, even if it's for something well above and beyond what I actually need.