If you want to keep it on the cheap, consider giving the pan a coat of POR-15, you can fill some of the larger holes with fiberglass patches embedded right in the POR15.  
POR15 is great stuff, I used it to patch and coat the trunk on my Spitfire about 10 years ago.  It still looks like new.  You can get POR15 on eBay or a lot of online places.  Fiberglass patches are available at pretty much any auto-parts store.
One thing - if you do use it, PLEASE use a respirator or do it outside.  POR15 gives off some seriously toxic vapors.  It contains isocyanates, you don't want to mess with it in a poorly ventilated area.