If you hunt around you can find just a Blythe head and eye mechanism. I ended up paying about half of what I would for a full Blythe but that was because I'm familiar with the usual body they use and knew I had a decent substitute and could make her an outfit. I wasn't happy with the wigs on the Blythes in my price range so knowing I was going to replace it I stumbled upon the white one. In my doll adventures I never intended to get a Blythe, don't care for the big head look, but she's here now and I've been able to answer quite a few questions.
The one thing I do know is serious Blythe people avoid the ones from the Franklin Mint, so you might be able to find one of those reasonable if you aren't sure or just pass on them.
For knock offs there are Basaak dolls who have received decent reviews from Blythe collectors. Basalks are said to work better with a body change. As shown in another post the Moxie Teen gives them a good look.