Heater - they're usually only about $20-$25 ... if you have more than one in the main tank, try borrowing one from there, just make sure the main tank's temp doesn't drop.
Filter - buy a cheapo power/sponge filter (petsmart has cheapy top fin ones) or a whisper. They're about $30. Or, find someone with some hanging out. You'd be surprised, I have 2 whisper 40s and a pengiun biowheel just hanging out from past tanks, so I'll be set for my QT
. Point is, you never know what people have, so ask any friends you have that are into fish. If you need to wait to have the $55 or so it'll cost, I'd recommend waiting. It's definitely worth it.
As far as everything else, just something for them to hide, and you don't even NEED a substrate, from what I've read. Just keep it clean and don't overfeed. There's a good article on a QT
tank in the articles section. It's here:
125 gallon saltwater: 55gal sump, 4 Blue-Green Chromis, Purple Tang, True Perc, Firefish, Royal Gramma, 5 Ricordea, Bubble Coral, 15 Pulsing Xenia, Green Star Polyps, Deresa clam, Green-Tip Torch Coral (about 11 "heads"!), Orange Montipora Cap, Purple M. Digitata, Green Slimer Acro. Yongei, 3 Orange M. Digitata, Pink&Green Acro. Millepora