Hiring Russian aerospace engineers worked out great for me so far, but I'm not sure I'd recommend the process to most startups. The biggest thing is that the geniuses that speak English well have all left Russia for various reasons. That leaves you with either non-geniuses, or geniuses with poor English. Usually, they've tried to learn English themselves and didn't get as far as they'd like, so "just hire a language coach" isn't a simple solution here. If you just want a lot of average engineer bodies, though, you can get that for cheap. I imagine it'd be ideal for something like building a tunnel or a bridge, with a lot of routine calculations and established design procedures.
The other big thing is the hiring itself. I got extremely lucky - I'm good friends with a great Russian technical recruiter living in Moscow, who was able to actually find people for me. But even with that huge advantage, it was tough.
If anyone has questions about the process, ask away - the idea of hiring expert engineers/programmers from cheaper countries has always fascinated me, and surprised me with how difficult it is.
Language barrier is not a problem in my case, I am fluent in both English and Russian. I know one can get cheap engineering talent in Eastern Europe, was more curious about your startup idea.
Anecdote 1: I have a translation of a Russian book of high school physics problems, most of which I can't solve.
Anecdote 2: Michael Spivak's "Calculus on Manifolds" is famous as the hardest math textbook an engineer will have to tackle. Well, there are major theorems in that book that are "easy" exercises in Vladimir Arnold's Mathematical Methods of Classical Mechanics.
