I prefer internally-shifted hubs to externally-shifted derailleurs because chain alignment always stays true with internal.
I completely agree with Aleman, internal gears are much smoother and less hassle.
I am on my 4th NuVinci hub build right now and my personal ride sports one with ~400 miles with a tricked 66cc 2-stroke on it as well.
When it comes to prices the NuVinci is about on par with an 8-speed hub, or if you were lucky and scooped up a few Cadillac Fleetwood bikes that come with the NuVinci and a disc brake for $300 like I did you could just pull it's wheels and put them on whatever you wanted like I did with one ;-}
3 speed internals aren't bad, my bike originally had one and I put a lot of miles on it just fine, I just wanted a little more control.
Derailleurs do work though if they are in Tgood shape and generally you don't need the lowest or highest gears anyway, but the big problem with an 8 speed is how thin the chain is. It doesn't take many under power 'bad shifts' to rip that chain apart and leave you walking.
Though I haven't tried one yet, I would a 5 speed would be good, you could at least use HD 410 for the drive chain.