Ballpark figure for a shed base 5 x 2.5 m. Dig out to, say, 150mm, hardcore, membrane, flags, sand an cement. Normally I'd give it a go myself but injury, long term, prevents me from doing so. Northern, rather than, London/southern-centric pricing.
Any ideas?
We got quoted just over a grand for 4.8 x 3m (midlands)
We went for a different option instead (wooden base supported on feet on paving slabs)
We paid £650 for 10' x 12' concrete base (Bedfordshire).
Paid £460 for 3cubic metres of concrete on a 5x4m base. Did all the other work myself, shuttering, sand, MOT, compacting etc.
our local shed place charge £99 for concrete pedestal things, £250 odd for wood platform or £600 for a concrete base to be laid. The contractor who's doing our driveway quoted £670+VAT.
To fit a 8x10 shed so somewhat smaller than what you're looking for. I'd do it myself if I had access to a digger as it's that bit that puts me off - hiring a mixer and doing the shuttering etc more than happy to do it. Digging through the roots and hardcore that makes up the bulk of our garden. No thanks.
Four of those metal fence post base things, four lengths of 4x4 tantalised wood plus four short bits to fit in the bases. Knock up a frame and job done for well under £100.
£250 for a 12' x 6' over here in deepest darkest Lincolnshire, but he didn't really dig it out, more of a pile it up and then concrete the edges.
Roughly the same size as what you mention, although not dug down much - soil levelled with the excavator, compacted, hardcore and sand compacted, then concrete slabs laid into cement/mortar mix.
100 quid, because that's what friends are for...
Free 2x2 slabs off gumtree tonne of sand dumped in drive by builder chum. 1 teenage son looking bored was biggest cost £20 for his helpful assistance