I don't think it is worth the hassle of getting a cheaper gun and then retrofitting a stock. For sure you want to get a heavy varmint barrel and AccuTrigger. If you go cheap then you will probably want to change out the plastic trigger guard for the metal one that comes on the BTVS, and you have the hassle of fitting an aftermarket stock. I've seen lots of issues reported in doing that. Some of the guns come without a recoil lug as well. All in all, I would just go with the BTVS right away. Has nice high cheek for a scope, and works well on targets.
Here is how I bedded my BTVS:
http://www.rimfirecentral.com/forums/showthread.php?t=223949
And here is how I got the trigger down to under one pound:
http://www.rimfirecentral.com/forums/showthread.php?t=227014
It shoots fairly well. Here are some groups at 25 yards.