Plenty o' options out there for you Revv.
As you mentioned, you can't swing a cat by the tail with out hitting a "guitarneck.com" site. Most that you have heard of... On this site and many other forums as well.. will have quality product.
Find a local luthier, likely they have purchased necks from many sources and they should be able point you off in the right direction. Do the luthier a favor... Where ever you get the neck.. Let the one who advised you dress the neck. One good turn deserves another.
At my local shop (not the Box o guitar franchise) there are guitar necks everywhere, some are as twisted as a pretzel, or broken. Those of course are the novelties that people look at and go "Damn how'd that happen". However, my local shop has necks that have been disembodied (sp?) for one reason or another. Typically they come from folks swapping out a stock neck for a different one... Looking for that tone I suppose.
Down side to putting a new (body-less) neck on a guitar....
You can look at against the light, rub the fret board, look at it against the light again, rub the back of the neck, look at it in the light again.... in other words, it's a lot like looking under the hood of your car after it stops running even though you know nothing about car engines... It just seems like the thing to do.
Typically, in most cases, you get what you pay for. This may not be the case 100% of the time, but it is typical.... It is VERY difficult to know the feel of a neck when it is not on a guitar. You just gotta hope for the best.
An option to buying a neck while still attached to a guitar... It is my understanding that the necks on inexpensive Strats, perhaps even some older Charvel and Jackson Strat "Copies" feel really great and play quite well. In other words, hit the pawn shops, local shops that takes in used guitars and test drive away. Do the homework and check the scale and sizes of the neck and make sure it will fit the guitar and if it feels right.... Drop $150 - $200 on a used guitar only for the neck. There are some diamonds in the rough out there.
Spend roughly the same amount of money, pick one up from a company (with a decent reputation and has been around a while) that sells guitars / bodies / necks.
IMO.... Stay away from Ebay.... I found a neck being sold by an individual that had lots of sales, good feed-back etc... I sent an email to him asking him to call me... I asked what did the neck come off of.... His answer.. a guitar....OK.... Not his fault... but he did not know SQUAT about what he had. I asked if it was twisted any. Answer... Naw... It seems to lay pretty flat on the floor....
Enough from the bus.....