If you decided to build a compost bin alp using concrete blocks you could design it a bit larger; try it without insulation and if it's not performing as expected then add internal insulation but perhaps lining with cheap pallet timber might work; building insulation isn't cheap;
It all depends on how much you plan to spend and how big a compost bin you need? If you include an adjustable vent in the lid then you could regulate the generated heat? This vent could be a simple large diameter hole in the lid with a cover secured by a single screw allowing the cover to pivot around the screw exposing more or less of the hole?
I'm unsure if I'll bother making a compost bin this year due to the bad weather making working in the garden a misery; I could make a sectional wooden compost bin in the workshop then assemble the bin up the garden.
I've just had a quick look at our local treated timber suppliers price list alp out of interest wondering how much a compost bin would cost using new treated timber?
Very roughly a 4' square bin at 4' high with a lid would need the following timber;
3.6 x 150 x 22 at £6.39 each
14 lengths in total to give four sides and the lid.
Roughly 3 pieces out of each full length and 40 pieces x 4' needed? £89.46
https://www.jobearnshaw.co.uk/wp-content/uploads/2017/06/EARNSHAWS PRICE LIST 2017.pdf
Corner supports and lid braces would add to this but for about £100 a new wooden basic compost bin at 4' cube with no base isn't too expensive? Galvanized nails would be used and these are cheap enough; as I say this is just a very rough estimate and is for a fully boarded heavy duty bin; the wooden compost bins I've just looked at on eBay are "slatted" so if a slatted bin was made it would be cheaper; our neighbour has a plastic compost bin which is sealed and she tells me it gets very hot; I'm not yet into serious composing but would an open topped slatted bin heat up?
I'm just doodling kicking a few ideas around.
Kind regards, Colin.