£2,700 is what we paid, and that is with an existing chimney, in good condition. The stove itself was included in that and cost about £700 retail.
You would get through more than two logs a night - think more like 4, split hardwood pieces, if you got it going about 7pm and kept it going until 11. And that's conservative. Solid fuel might work out cheaper. What would you do on cold winter mornings? Would you be happy to be cleaning out a grate and laying a fire at 7am
? there are some you can get that burn overnight, but IIRC these tend to have larger outputs.
You can have wood delivered, but you need to find a good source and it needs to be well seasoned. Tis far cheaper to buy it in large quantities and so you will need to have storage space. Around here (London outskirts), 1 cubic meter of good seasoned wood costs about £120. Kiln-dried wood is more, but you don't necessarily need that and it burns really quickly I find.
We have a small burner (about 4-5 kw) and this heats living room, dining, and hallway.I absolutely love it, have to say.
You will need to have the chimney swept every year at least, but that's probably not a substantial cost.
I am not sure that UFH costs a lot to run - especially the wet underfloor type. But this would possibly only work if you were considering replacing all the flooring. There might also be considerations given the fact it's a top floor flat. I'm not sure how it works if there are people below you.... I don't really know much about it TBH but a good plumber should be able to advise.