I can appreciate the limited budget, especially with the aquarium hobby draining the wallet! ahhahaha...
What's working out for me lately is to buying used. There's some good tools out there that'll read the number of shutter actuations as that's the big issue with buying used digital SLRs... the shutters fail due to the high number of actuations so if the previous owner uses the thing like a gattling gun, it'll cost you to repair it. Regardless of Nikon or Canon, I'd look out for that if going used.
But check out this on the Nikon D90... it's cool.
D90 Demo