i. take the fork apart to see if it can be fixed/maintained to it's original condition. Wouldn't this be a nice time to be with your son? And it shouldn't cost any dollars either. Of course this may depend on whether or not your are a tinkerer or not, or whether your son would be interested.
ii. Depending on what you find from i., rebuild it or buy a new fork.
Incidentally, I bought a Manitou SX-R 00 fork back in 2003 for just over a $100. I'm not an extreme rider by any means (actually, I'm gentle) but I think the SX-R along with its tunability ranks high for me (pre-load, damping and compression adjustments). I still use it today, and I find it's pretty darn good (well, caveat here, at least for me!). You might be able to get one of these forks on ebay cheap, though travel is limited to 80mm. Maintenance is pretty easy too, I stripped the fork to put firmer springs in it.