For a pair of clowns I wouldn't do smaller than a 75l aquarium. Assuming you want to skip corals it will make this build a lot cheaper.
To save money on live rock you could go with 10 lbs of dry rock from bulk reef supply.
You can also buy a HOB
filter instead of powerheads.
Not counting the price of the tank and stand you should be able to get everything you need for $100 but that is a very very basic and simple setup.
Basically with salt water, the smaller the tank the more difficult it is to maintain especially when you don't have a refugium / sump. I would suggest waiting and saving up to get a properly sized tank with sump to make your life easier.