Chas, you sometimes pay as much or more for a used boat than you will a new one...just because the previous owner wants something for building it.
If you are into building at all and if you have built and flown an RC plane, you can dang sure build your own sailboat. Sailboats are not nearly as difficult to put a kit together as an RC airplane. If I were you, I would just pick a kit and build it rather than buy someone else's problems.
Some excellent kits are the Thunder Tiger Victoria, the Thunder Tiger Voyager, the CR914 and the Kyosho Seawind.
The Victoria is the smallest of these boats at a bit over 30" and 4.5 lbs. It's a good honest little boat and very popular. There are a LOT of "hop-up parts" available for this boat and most serious Victoria skippers change a lot of things and make this into a serious little racing boat. It IS an AMYA recognized class and, in fact, MOST of the country has Victoria fleets and organized regattas. Point being you won't sail or race alone.
The Voyager is a 1 meter boat but not a recognized class in the USA. Some clubs race a 1 Meter "Sport" or "Open" Class where this boat would be allowed. It's a beautiful boat and sails well. Some really pretty pictures of them on this forum in fact.
The CR914 is a 36" boat and like all of these is available in kit form. It has a fine reputation as a good sailing boat and a lot of enthusiastic supporters and a good owners association. (As does the Victoria)
The Seawind a 1 meter boat, 39 inches, and is a fairly new AMYA class boat and VERY STRICT one class design. (As I believe the CR914 is also) One class design boats supposedly means everyone gets boats the same place and builds them the same way so that all boats are the same potential. However, many so called "one class design" boats have so many exceptions that a skipper can do to his boat that the reality of it is anything goes short of redesigning the hull. The Victoria is a good example of this.
However, the Seawind is strict. You build it with what's in the kit. The good news is everything in the kit is good quality stuff. In the long run, the Seawind probably ends up being the least expensive of ALL these boats.
The Seawind is a sleek, fast boat and like the 914, it has a terrific Class Owner Association with it's own newsletters/super support etc. A good class owners association becomes your family when you get a boat. They help you and support you with whatever you need to make a success out of your boat. They also are a free source of information for virtually everything you can do or everything that has ever been tested on your boat. So they are worth their weight in gold to any new skipper.
Any of the above boats and you will need at least a 2 channel radio. One of the servos MUST BE a high torque model to manage the sails in and out in strong winds. At least 100 oz torque.
IF you aren't familiar with it, bookmark the American Model Yachting Association, AMYA, at
http://www.amya.org/
Get VERY, VERY familiar with everything they produce. Better yet........join them. Their magazine alone is worth it. The AMYA is basically the "Mother Ship" to all of us RC Sailors. It keeps everyone together and keeps things from going crazy and gives us all some clout with venders etc.
Hope some of this helps. One thing you sure have correct is READ and learn all you can about all of the boats and then you can better decide what's best for you.
Let us know if we can help in any way. All of us welcome you and are eager to help you succeed with the boat of your choice.
Jim