If you are castrating for sure the younger the better. They heal quicker, there is less swelling and it is an easier proceedure (Can't tell you how many little guys I have put under to make them great geldings). I have assisted with castration as early as 4 months to as old as 20 years. Those little ones just do better. If he is a routine castration for where I am you are looking at about $300-350 including drugs, outcall, etc.
If you have a crypted orchid you are looking at a minimum of $1500 and it can go up from there.

Hope this helps