Nice Mom! How old is the son?
There are a lot of new boats that they can get in to for $20K, and the sky is the limit on the used front.
A few to think about
:
Maritime Skiff 1890 (as mentioned above) - fully loaded with an Evinrude 90 FICHT or Honda 90 will run you around $21K, trim the options back and it's less. Simple, solid boat with essentially nothing to go wrong.
Key West 1900 - these are available factory rigged with a Yamaha 115 4 stroke and on a trailer for $20K.
On the used front there are many 17' and 18' Whalers, Scouts and Edgewaters that can be had in the $15K-$20K range. Check out
www.boatttrader.com, www.bestboatbuys.com and
www.capecodtimes.com classifieds for some used boats.