Like Aliamyz I too have tried putting a discarded candy near my neps, and the next day lots and lots of ants, some of them of course would find the pitchers and "explore" inside. Therefore I agreed to a view that keeping neps around house doesn't kill off all the insects in the area, but maybe rather attract insects to where they are!
If you want to spend for the food, my vote is Crickets, but I really haven't spent money on my neps to feed them. The most active feeding I have ever done was to catch some coackroaches to feed to my VFT, and I have stopped that already too!
TTFN
Arvin