I'm a Luthier... I build on occasion, but primarily repair. I've been doing this a long time. From before there even were any aftermarket parts at all!
The first replacement necks and bodies I saw, were Mighty Mite, and Schecter. Began in the 70's. I've modded many instruments with Warmoth necks. A few bodies, as well. The quality- is top-notch. One thing I distinctly remember, is that during the early years, you could build a Fender Bass- a lot closer to the style and combination of parts than you could order and upgrade from Fender, for a lot less money. Now, that is not the case. The other point, is after laying out as much as 2k for parts and assembly, the resale is just not there, if you decide you don't like it as much as you thought you would. I still have one Warmoth build as a personal bass. Swamp Ash, maple neck, old Fender P-bass pickup, and painted Dodge Viper blue. It's a very good looking, high quality, great sounding bass, and ironic, I don't play it that much.
Perusing the Warmoth site- the prices of their parts now, are pretty up there. Still - very high quality stuff.