I agree with this. I wouldn't have any exact numbers and it depends on the bow company, but I would guess that by the time you spend on average $100 for strings and cables and another $100-150 on cams, not counting press fees and whatnot if you don't do it yourself, I think a safe estimate would be anywhere from $250-300??? I am just guessing, I haev never done it myself I guess. Good luck.
I have done it myself, and unless you really know what you're doing, your better off going to the bow shop and ordering specifically what you need...
To give you an example, a buddy of mine took his Hoyt and switched from a Cam1/2 to a Spiral cam here is the $$$:
New Cams- about $85 from the classifieds (not sure about cost for new ones from Hoyt, but I'll guess $150ish)
Strings- anywhere from $110 down to about $60 (I think that's what my string guy gets, I haven't ordered any in awhile).
New limbs (he lost 14 lbs of peak weight when he switched cams)- I've seen them from $100-$120 for XT 2000s in the classifieds- guessing $200 plus new...That's a total of $246-$460 before ever paying for a shop's labor (and hopefully) expertise...
You would be better off buying a new one that is exactly what you want then pay $400 for a used one then drop all that $$$ to get it there...