It depends upon the AGE and what type of Bonsai it is. I just paid about $200 for a 17" high Chinese Yew (Podocarpus) that is 13-years old and I think it was a fair price.

Better (and less expensive) choices for beginners would be Hawaiian Umbrella Trees (dwarf Schefflera) or Ficus (various spp). 14-18" tall specimens of these bonsais should be available for under $100.

Of course you could also opt for a very large Juniper in a nursery container for maybe $40 to 50, style it then get dad to pop for a decent pot for it?

Along the way you'll get your hands dirty, learn a little more and be able to say you actually worked that tree to the form it's in. Just my thought.

Bob