If you're doing this purely for economical reasons, then forget it. As others mentioned, IV coke lasts only a few seconds. As for crack, I personally find it inferior to snorting coke - on par with sniffing glue, perhaps (and no, it has nothing to do with the purity of my product since I IVed some of the same rock I smoked and it was great).
IV coke is, in my experience, definitely more addictive than snorting coke in the "immediate" sense. After about 3 shots, I found myself going into autopilot, preparing a shot as soon as the last one ends. This is why I stopped IVing coke after just two runs. The only time I would ever IV coke now would be in a speedball, and I'm lucky if this happens once a year.
If you want to save money, I suggest going with a longer-lasting stimulant (if you must)...