ORIGINAL: burnineyes
But unless you are getting these packs at some major discount, it sounds like you have not done your research. Most average Nimh packs normally cost more than a good quality lipo from HobbyKing, a high quality Nimh pack is usually double the cost of a good lipo.
It's true lipo packs can be less expensive than really good Nimhs. But that does not take into account the other accessories needed to go lipo. If you are set up for Nimh then you'll need to get, at the minimum, a new lipo capable charger and possably a ballancer. Those things can make the switch a more expensive proposition than just buying different batterys.
Still, if it is at all possable, save up for a while longer and make the switch to lipo. The advantages make it well worth the wait.