I'd be wary of straightening an axle. I've seen too many broken ones to trust their strength after a bit of bending. Sounds like you've got a spaghetti al dente steel piece of crap. Running freewheels rather than cassettes produces more strain on the axle, so you might want to think about switching. Also, if the axle is bent, you may have twisted the dropouts, so that's worth checking out. I'd go for a higher quality "BMX" level strength one (in cromoly) - if you're lucky you might find a BMX one with the same dimensions/threads.
I'd be wary of straightening an axle. I've seen too many broken ones to trust their strength after a bit of bending. Sounds like you've got a spaghetti al dente steel piece of crap. Running freewheels rather than cassettes produces more strain on the axle, so you might want to think about switching. Also, if the axle is bent, you may have twisted the dropouts, so that's worth checking out. I'd go for a higher quality "BMX" level strength one (in cromoly) - if you're lucky you might find a BMX one with the same dimensions/threads.