bump your budget up just a little (80-100 used), I would recommend an Audix D-4...sounds great on floor toms...as well as on many other sources (bass, brass, kick, guitar amp, etc.). It's actually one of my favorite instrument microphones.
i bought an akg d550 from a friend a few years back, tried using it on kick but it sounds awful there. but it's surprisingly nice on floor toms. i think you might even find that one NEW for $60.
Someone suggested the ATM 25 and that is my #1 preferred kick mic. I got a deal on an
AT Pro 25 (which is the "student grade" of the ATM 25) and it also works okay on kick(in a pinch), but I found it to be superb on my 16" floor tom.