Whatever the cheapest option is, I'll generally go for. Most repro carts are $25 - $40. If the original is a lot more expensive than that and I have to have the game right now, then I'll get a repro. My Earthbound is repro, and to be honest I'm glad that I didn't spend the money on an original copy - wouldn't have been worth it to me.
I think a lot of collector's feel like it's cheating. Some have said they don't even like the idea of the original publisher printing more, and would prefer the re-print to be distinguishable. That's a level of collecting that I don't get into. It's not the age, assembly number, or scarcity of item I'm interested in, it's just the physical media format itself.