I think the best cheap speed controller I've used is the electronize, easy to get in uk, pretty cheap and really rugged. Main critism would be size as they are quite big and no built in mixing but most tx have that.
I've also tried the sabertooth an although it is quite compact and has lots of features they are not very rugged, have to get them from america if you want the guarenty so large import charges and can't be pushed to their limits. But they are more compact and very simple to use.

I have no experience with the marine escs but they are even cheaper which I think is better because at end of the day if it makes a motor go back and forward that's all you need an in a robot which is supposed to get destroyed why spend more than you need to?

I also haven't used the more expensive controllers so someone else will have to give their opinion on them