Concrete – Cinder block or concrete for shed basement

I've had an almost exact scenario.

you basically have 3 options 1) spray foam the entire system. Expensive for small areas. 2) 1-2 inch foam board that's cut out exactly. tuck tape the seams to the joists/ceiling. This would be a pain to mitre. (I don't think they're meant for this) 3) batt insulation with 6ml vapor barrier over, then tuck tape the seams to joists/ceiling.

Each have pro's cons. spray will be best seal. Batt insulation would be easiest to cut/work with and seal.

Good question. Under the circumstances, I feel you would be better off leaving the existing insulation alone, or simply cover it with a more attractive plastic sheet or some inexpensive fabric. perhaps a curtain type wall over the insulation? If you remove it without a plan to replace the insulation, the basement will be somewhat cooler. There are several ways to insulate the walls without framing, but adhering rigid foam insulation is expensive, up to $80 per 4X8 sheet, and spray on foam is more expensive than that and should be professionally applied.