How much work is it to add radar on a small sailboat? Is there much wiring,
does the radar need much power, and about how much can this be done for?

It's not a big job by any means. And with the new smaller radars the power draw and costs aren't bad either.

Check prices he boatfix.com

How much work is it to add radar on a small sailboat? Is there much wiring,
does the radar need much power, and about how much can this be done for?

It depends of course. You can get an adequate radar for less than $2K,
and they typically draw 10 to 15 amps when actually operating, much
less in standby mode. Look on the manufacturers web site for the
detailed specs.

Professional installation can easily run another $2K, much less if you
can do the work yourself. I self installed a relatively complex Furuno
system on my trawler last year with about 15 hours of work and a $300
mast bracket. It does require some experience working with mechanical
and electrical components however, and if you get into trouble, will
probably do bad things to your warranty.