You could go with a 29G tank as the obsolute smallest size for what you want. 40G would be better for your wants. HOB/Canister filter if you wish, but put in your own media of choice, not the ones made for them, save you $ and work better. You can actually get to the point you don't need a filter with enough Live rock but IMO filters are always good if you keep up on maint. You will need a powerhead or 2 in the tank, something like a Koralia2 or 3.
But in a 29G you shouldn't have a problem if you keep up on waterchanges with good RO/DI water + salt mix and proper lighting for an anemone. 4x T5HO should suffice for a Condy or Bubble tip anemone. Both black and white clowns and royal grammas tend to lean just slightly on the agressive side and need their own space so you can't crowd them with too many fish, but if all you want is a clown and gramma I think those 2 would be fine by themselves with an anemone in a 29G.
Parts:
Tank
Heater
Live Rock (Sand optional)
Powerhead(s)
Filter (optional)
Lighting
Protein skimmer (optional but highly recommended)
Bare minimum, buying just the essentials brand new, I would guess the price would run about $560 for just the tank (50), light (250), heater (30), powerheads(40x2), and rock (30lbs x $5lb=$150).