A 55 is probably one of the worst footprints for marine tanks regardless if FOWLR or a reef due to the narrow width. It seems like large tank but really isn’t. Also many 55s have tempered glass so drilling is out.
Also I would skip the tangs due to size requirements and behavior (yes I am a firm believer in buy fish for the tank you have and not the one you will be buying in two years).
Because you are on a strict budget of $500 if this did not work out, you could do the petco $1/gallon sale, if you have any DIY skills or know anyone build a 2 x 4 stand and skin it and a simple canopy to house shop lights from HD, use one of the recommended HOB skimmers and a powerhead or two and you would be under budget:
Tank 55 gallon though a 40 breeder is a better footprint to be honest even though it is smaller: $60
Stand and canopy: $50 to $75 (most store bought stands are particle board and are “ok”)
Lights: one 48 inch shop light is $20 and add in bulbs for a total of $40.
Skimmer: $200
Powerhead: $50
Heater: $25
Rock: $50?
Skip the controller and buy it later on if necessary.
You said no sump so no plumping, return pump, no wet dry system.
That is just under $500 but $10/gallon is pretty cheap in this hobby.
The other option is to look around in the for sale forum/cragslist for a little larger tank such as a 75, 90, or 120 and you could swing your tang then if you went 120. Of course the downside to that is you are over budget unless it is a complete turnkey system that someone is dumping due to a move or divorce for example.
Good luck.
