Chris, there is no end to the good boats that have been designed and are out there waiting to be built. Myself, I would offer some rules of thumb in a "stream of consciousness" form.
1. If you are thinking seriously of singlehanding, read everything the Hiscocks have written. They weren't single handers, but they sailed as if they were. A lot of practical experience in their cruising books.
2. Plywood has no place in a proper boat larger than a rowboat, and even then, only junky ones. (I can hear the howls now, but them's the facts.)
3. Plans touting they produce "easy to build" boats generally produce crappy boats. Good designs aren't marketed based on their ease of construction, even if they are easy to build.
4. Keep it simple. To the extent anything on a boat can be simplified, so much the better. Store-bought gizmos will fail. Complex systems require continual maintenance in the marine environment.
5. Indigeneous working watercraft which have evolved over generations are almost always the best choice for their local waters, or waters similar to that. (They are also often "easy to build!")
6. You get what you pay for. "Cheap to build" yields a cheap boat to begin with. "Cheap to operate" is much more important than "cheap to build."
7. Be realistic about your limitations, especially if singlehanding. There is a limit to the size of a sail one man can handle. Same with the size of the boat. For example, beyond a certain size, 30' perhaps, one man can't handle the ground tackle. The right sized anchor and chain (mandatory anywhere there's rocks or coral about and preferred elsewhere) simply become too heavy. So you buy a manual anchor windlass, which ain't cheap... or, God forbid, an electric one... which means heavy battery capacity and charging ability... and, you see where it goes?
8. Standing headroom and an enclosed head are very expensive luxuries until you are into a 40' or larger hull. Really. "Bent headroom" is more than adequate and available in most 25' and above displacement hulls. You sit and sleep below and you work on deck. The cost of a doghouse is the loss of the ability to carry a rigid dinghy on deck (unless you want to lose your foredeck and have no place to handle headsails and ground tackle.) If you must, you can "enclose" a head (bucket) with a curtain or a closed companionway door. If you are singlehanding, what's the point?
9. Always build a boat with an eye to taking it apart some day. This will need to happen as time passes. This is not much of a practical option with cold molding, strip planking, plywood, epoxy adhesive laminated hulls and so on. Always assume that if a crusing boat requires major repairs, the need will arise in some God forsaken place way behind the back of beyond. Don't expect anybody to be able to weld your stainless or aluminum in a local native fishing village. In this regard, hand tools rule.
As for boats and their ease of construction and low cost, look no farther than the home waters of your youth. The British Isles have any number of fine fishing boats from the last couple of centuries which make excellent cruising boats. These aren't limited to the now-famous Bristol Channel Pilot Cutters (nor any number of knock-offs that may look similar above the waterline, but are not at all the same thing. Sorry, Mr. Hess, but your "BCC's" aren't even close, even if they are nice boats in their own right.)
Consider, for example, the West Cork Mackerel Yawl (a cutter, actually, but called a yawl locally.)
Her lines are at: http://tradboats.ie/project//Userfil.../linesplan.pdf
Or the Connemara hooker:
Lines and photos of these classic gaffers can be found on line (free to use) at the Traditional Boats of Ireland Project website. http://tradboats.ie/project/ The book "Inshore Craft" is chock full of similar boats from Scotland and England. These boats can be built with little more than hand tools, as they traditionally were. All galvanized fastenings. Very little hardware. Suitable for an outboard, or an inboard engine if you want to get fancy. Limited, but very efficient sail plans which are easy to singlehand. (Those fishermen were not fools!) These boats can be finished "workboat fashion" and look quite smart, or, if you wish, "yotty" with varnish and all that. They have a lot of volume and you can provide for standing headroom and a "powder room" if you must.
What is remarkable about these boats is that they require little or no lofting or complex bevel calculations. They are "lofted on the stocks," with patterns and measurements taken from battened molds. All one really needs is the stem shape, the angle of the stern post, and three sections. You can build them to whatever size you require, using the rules of thumb for their design. Everything else flows from there. There is a great small book and DVD which shows a fellow building a 35' hooker without much more than a thickness planer, a chainsaw, and hand tools. It is really worth a read. The lines for the boat come with the DVD. http://www.irelandonfilm.com/nasaora1.html I dare anybody to watch that video and not want to build a boat! It's a great confidence builder.
Anyhow, you'll do what feels best for you in the end. Boats are like wives and waffles, you usually have to throw the first one out before you find a keeper.