Let's take a step back. Live Rock is NOT required for a saltwater tank. It greatly enhances the look of the tank , adds biological filtration and is required for some livestock (or something similar) feeding patterns. You can run a pure sand bottom or a bare bottom for that matter. If you choose to use rock, you can use it a pure decoration or add it in quantities that will allow you to use it for filtration. If you choose not to use live rock then you need a canister or HOB
filter (with the size of your tank probably multiples of those). You also don't need any specific lighting if all you plan on having is fish. A protein skimmer is a great tool as well but not required. Plenty of successful tanks have neither.
As far as the fish are concerned, they should be taken back if possible. Cycle your tank fishless. Get the right water testing chemicals, do it right, then add fish.
You don't need to spend an arm and leg to get into saltwater. If the passion takes then in the long run you'll start looking at other species (coral, inverts,etc) that require specific lighting (read that $$$$), and other semi-required equipment to make their survival more likely.
Yo do not need to make that leap now if you choose not to.