Poundland, 250g for £1 Probably need to run twine and foil strips, or a fleece cover, otherwise the birds will probably eat it or sieve some soil / compost over it, and then dress thinly with grass clippings. Won't grow if it's more than thinly covered, so a clear plastic or garden fleece held up a little on sticks may be the best answer
any seed, chuck abit of topsoil or compost on the top to stop it moving. then water everyday if its not raining. will grow quick then :)
I've just done loads of patches (27) where a dog I was looking after killed the grass with her urine. I just used loose seed from a local diy store. Sowed it on a Monday and most of it sprouted the following Monday, looks much better now :)
https://www.wilko.com/en-uk/wilko-multi-purpose-lawn-seed-with-ryegrass-500g/p/0341281 worked within 2 weeks
But the loose seed in store, you weigh it and bag it up yourself. 1/2kg will do you - from memory it''ll be about £2.75.