I admit that sometimes I find it a pain spending an hour or two assembling a piece of furniture or such. One of Mom's neighbors regularly calls me to assemble something she has purchased. So, I'd probably pass on buying a thousand dollar "ready to assemble" kit that required clamping, welding and painting.
That said, there may be a market for things like tractor buckets and backhoe buckets that are 90% assembled, but missing the mount. Perhaps you could also fabricate custom mounts for a variety of backhoes and loaders that would be ready to be welded in place.
Of course, another option would be to have a portion of your business dedicated to custom fabrication.
So, for example, someone here was looking for a Ford backhoe bucket.
http://www.tractorbynet.com/forums/attachments/276139-new-holland-backhoe-replacement-bucket.html
You could have a stock bucket that you would just fabricate the mounts, weld them on, and ship it out... ok, so not "do-it-yourself", but providing a valuable service.
Same thing for tractor buckets, and bucket forks that might be mounted on dozens of different loaders.
It looks like you already do that to some extent.