Even if you recap the needle, the opposite end is still open. There's a reason they come from the factory in vacuum sealed bags. If air can hit it, there's a risk. If bacteria gets inside the needle and you draw with it, you'll be pulling the bacteria into your injection dose. In fact, you want to go from opening the bag to injecting ASAP, because any time in the air is bad. Imho reusing needles is a terrible idea.
Not only could you look forward to a nasty abscess, but you could get cellulitis:
http://www.thedoctorltd.co.uk/inject.html
A staphylococcal abscess occurred in a 24-year-old bodybuilder who reported, for financial reasons, reusing needles on multiple occasions.(6)
Two case reports of staphylococcal gluteal abscesses developed in young bodybuilders 18 and 21 years of age. The steroids were injected by other weight lifters who were not familiar with sterile injection technique.(7)
Pectoral and deltoid abscesses were reported in a 20-year-old AS injector who had injected his AS preparation and then returned the needle to the vial to inject into another muscle group.The patient was thought to have contaminated his multi-dosage vial with skin flora and subsequently spread the infection.(8)
Don't reuse needles. Just don't do it. Look at every other thread online where someone brings this up and noone thinks it's a good idea.
If you're worried about the shipping costs, then just buy a bunch of syringes and needles at once, that way the shipping cost won't be such a big deal, and you'll never run out of syringes or needles.