It also will be very linear will it?
My experiments with that system in the late 60s showed the actual control region was very small.
Vactrols are definitely limited in a lot of ways: not very precise, not very linear, and they don't tend to open or close quite all the way. That said, they're definitely cheap, and depending on the use case, sometimes they work just as well as a digipot would (or even better, since there aren't defined steps of resistance). Lots of modular synth guys love them because they allow you to replace pots with control voltages, meaning that pretty much anything can be taken apart and turned into a module; and for Arduino specifically they can be nice because they only need a two-wire connection, ground and PWM.
Really, I just wanted to mention it since nobody else had. Without knowing more details about the project OP is planning, it's tough to know what solution will work best, or at all.
Man I was. When ever people meet me they say "you don't seem very grumpy" to which I reply "it's my day off". However suffering fools gladly is something that is not my strong point.
Their is a world of difference between someone who does not know something and wants to learn and someone who knows nothing but thinks they do.
I understand that there's a lot of the latter around here (or around the Internet in general), so it's pretty easy to get frustrated about it. But let's be real, the OP was just lamenting the price of a part, which I'm sure we've all done. I don't think that really justifies calling them a spoiled brat that should take up knitting instead of electronics.
In any case, I'm not trying to start a flame war or argument here. It was just a friendly jab at what I perceived to be an over-reaction. No hard feelings?