I know someone who gave her twins balance bikes around the age of 2 and around 3 they were off and riding pedal bikes without training wheels.
In general, I think it's a good idea over training wheels. But some kids are into it and some aren't. It also depends on if you have the time and space where the kid can practice.
I have balance bikes for my twins, but I work so we don't get as much practice as I'd like them to have so it's slow going. One is more interested and seems to get it better than the other.
I also had to hush my Mom up because she kept saying "It's missing pedals" or "Where are the pedals?" and I didn't want the kids to suddenly not like it because it didn't have pedals.
But learning how to pedal is also a good skill. If your son doesn't have a trike, then it might be worth getting him a trike and defer the balance bike until the spring or something. I've been told it's not confusing for kids to have both.
There are lots of balance bike brands out there and some are cheaper than others. We have the Strider pre bike which is closer to $100 or less. Walmart has some that are cheap, but I have not experience with the quality of them. A discount site called www.zulily.com occasionally has them on sale. They have a sale going on now until July 19th for various bikes, including some balance bikes. You need to make sure you get a size that will work for your son. FYI, the zulily site can take weeks for the order to arrive so plan accordingly if you buy from there. No returns either.