Will my non-digital Canon lenses be compatible with a digital Canon SLR body?
Since the EOS 300V have an EF mount, then the answer would be yes. All Canon EOS lenses can be used to a Canon Digital EOS bodies – except if you’re talking about the newer EF-S lenses which can only be used in Canon’s APS-C DSLRs. So, I believe that your 28-105mm and 75-300mm will fit into the newer DSLR. For that kind of budget I would recommend an EOS 350D, or an EOS 400D if you can get it at that kind of price. These two are a very good camera and you don’t have to get a second hand camera with that kind of budget (well except if you plan to get more accessories along with your camera).