i get used wheels and tires cheep at a local junkyard.   I wouldn't pay more
than 5 or 10 bucks for a rim.  Then again, i have the impression that it is
junk they never sell.   Actually i have a pile of 14" bus rims i'd give away
(64-70)  Also, the yards have to pay to get rid of tires.  There was a
junkyard i went to that was $5 a tire (with rim likely as not), but you had
to dig to find the one you want.  

my 2 cents

clara