I'm not sure where you live, but you might be lucky enough to find a stallholder selling it in an anime convention. I found a few F/SN t-shirts in one of the conventions I went to, and managed to grab hold of this shirt
. I also saw a few MB/Tsukihime ones as well.
If your area doesn't have any anime conventions (or anime stores), I'm afraid it's gonna be quite hard to get any for cheap, if any at all.
["Here is wisdom. Let him that hath understanding count the number of the beast:
for it is the number of a man; and his number is Six hundred threescore and six."]
--Book of Revelation 13:18