IMO I would first see how much it would cost for a nice sump setup with a good skimmer and pumps. Then Price lights that will allow for you to add corals later on when the tank is well established. Also make sure you setup a smaller quarantine tank for sick fishes.Once your price that stuff out, you can determine what type of tank you can afford.
Also Live rock is very expensive and if you want to do a 90g correctly, it will cost you at least $600.00 to stock it with about 90lbs of Live Rock.
“I’m not an expert by any means and am probably the last person on here to be giving you advice, but there are things I wish I knew before setting up my tank that would have saved me money in the long run.
Just as an example:
Lets say you go with a 90g tank. It will most likely be 48" long.
Lighting:
I suggest PC lighting, but I am still new to this and someone may say MH are better. I think PC lights are the best price for the buck. Most good PC lights will cost you about $250.00+
Protein Skimmers are also a costly part of the system, but what I have been told by many people on this forum is to not skimp on this piece of the system. The nice skimmers cost $200.00+
Then you have your sump systems. You will want to get better advise on this part because I’m still researching about sumps. I do know you want a lot of flow going to and from the sump so you will need good pumps. Most sumps setups I have seen for a 90g cost around $300.00+ for the sump and pump setups with the proper plumbing.
Then you have your blowers. Also a topic I don’t know enough about, but I do believe you will want at least 1000gph water flow in your tank. If you use just the plain power heads as I do, it will cost you about $120.00+ to get enough for a 1000gph flow. I have a feeling there are better setups out there, but not sure on their price tag...
I also don’t know much about heater systems and I’m sure there are parts of the setup I’m leaving out, but at least you can see where I’m taking you.
If you buy the parts I have suggested you are looking at about $870.00+600.00 (90lbs Live Rock) = 1,470.00...
That doesn’t leave much money for your tank and tank stand, which will depend on what appeals to you visually... You can either get a cheap glass tank and build your own stand and hood or you can buy a nice acrylic setup with show stand....
So I would figure out the best price for all the parts to run either a 75g or 90g tank including enough Live Rock to start and then figure out what type of tank you want to buy...
Hope this helps...
P.S. I have a 100g tank with too little live rock running on only 600gph water flow and a basic bio filter with 1 10000k light and 1 actinic blue light. My tank has good water quality, but I have yet to keep fish in good health and have to monitor my water more than I would had I known what I do now about the parts my tank would need to run properly.
There is no cheap way about doing this hobby and if there is I haven’t figured it out yet... ; )