If the machine is in tolerable mechanical condition then that is a good price. Consider it a retrofit-ready machine. If the control(s) that come with it work for a while, that is an extra bonus.
Continuing to maintain and run the Boss 5 control will be challenging, but if you are patient and electrically-inclined, you can probably do it with the help of this group. Having a spare control for parts can't hurt.
Centroid retrofit kits are a good fit for these machines. They would probably be in your "medium" or "super deluxe" category (ca. $10K).
See
http://www.centroidcnc.com/bridgeport_boss.htm
Disclaimer: I am a Centroid dealer and technician. There are other nice controls out there too. There are less expensive controls too, providing you are prepared to do a lot more of the assembly and setup yourself.