Cross threaded crank help....

[boy in a kilt]

what you can do depends on how screwed up your threads are.

If they are just a little screwed up, and by that I mean it's just the first few threads are screwed up or stripped, you can use your pedal to re-cut the threads by screwing it in from the back side. If screwing it in doesn't start easy, back off and go to your LBS and have them re-tap as suggested above. I've done this a few times, although never with cranks.

A caveat though. Aluminum crank arms are fairly soft so if you choose this method, be careful about replacing the pedals. The first few threads are wont to be a little wonky.

A second option. If your crank arm is a relatively common make (e.g. Shimano 105), you might look around on CL or some such place for a used set (if you lived in the Seattle Area, I'd tell you to go to Recycled Cycles).

The problem with re-tapping your threads by any method is the receiving threads are now a little bigger than the pedal threads. What this means is you have fixed the problem for now but you'll need to replace the crank arm at some point in the future.