It's hard not to go too far on these "lego" guns. You will rarely ever get your investment back. But, I've enjoyed the tinkering making the investment worth it to me.
You can buy the parts direct from Crosman and it's way cheaper. It probably only needs the pump cup and maybe the O-ring for the valve. Usually a pump cup will get them running again.. around $2 from Crosman. On Crosmans site, go to SUPPORT. Go to OWNER'S MANUALS. Look up your owners manual and EVP. Click on PARTS DIAGRAM and find your part number that you need. For example, the pump cup part number is 760-140. Call Crosman customer service and tell them you want to order parts, they'll need the numbers for the parts you need. Cheap, and only $4 shipping on small parts. Good luck with the project, they're well worth fixing. Great guns