as far as cost comparison, I don't know what chroming costs since I would never have it done, but polishing is free. just do it yourself.
I would never chrome because:
1. it adds weight to the wheel, which is one place you especially don't want it.
2. it has the potential to weaken the wheel, which can lead to cracking, especially with wheelies and such.
3. it looks bad in my opinion
4. I wouldn't spend money on something that is going to lower the performance of my bikes. the cost outweighs the benefits.
5. Polishing looks just as good. gives the same effect (the gawdy Bling effect) but has less of a posuer attributes to it cause you didn't spend a lot of money to make your bike slower.