I suggest a 20-30 gallon tank. New costs maybe $200. You can probably find it cheaper on sale somewhere. Or find a used one.
As for fish, start with a male Betta to start cycling hte tank.
Add two varieties of tetras later on. Maybe 6 2 weeks after the Betta and 6 more 2 weeks after that.
Also get a Pleco to help keep the house "clean"
The last thing to add (maybe in 2-3 months) is an Oto Catfish. They stay relatively small but eat the lagae. Don't get Cinese ALgae Eaters. They are semi-aggresive. Oto Cats are moer docile.
I also tossed some glass shrimp (AKA: ghost shrimp) in my tank to help control the algae.
Also, toss in soe potted plants and a piece of driftwood.
Buy the filter and filter stuff online. Get the waterfall style. Always get the biggest one that yourtnk canacomodate. More filtering is always better and there is no such thing as too much. Also, buy the decorations and stuff online. It is muchcheaper! Food too. Buy it all in one shot then you get free shipping! Dr Foster's and Smith is a good place to buy stuff.