I'm an amateur photographer and I'm looking for a replacement for my Sigma 28-70mm lens, particularly the Canon 28-135mm IS USM lens. The problem is that I don't want to pay over 400 bucks for this lens. I've seen a refurbished one for $350 and a used one for $360, and of course the new ones for around $410. Can someone help with deciding between the refurb and the used, first, before I shelve out $400 bucks for the new one? Thanks!