I've just discovered
Quiltessential. They don't have an enormous range of fabrics, but they do have a vast number of Kona Solids* at £2.40 for a FQ, and I placed an order on Sunday and received it on Tuesday with very modest P&P.
The website is fairly basic, but the images are good. I didn't receive any email notifications of order placed or dispatched, and I don't seem to have been able to set up an account, and there's no Paypal option. They are a long standing company though, so this is inconvenient rather than worrying.
* They say "We believe that Quiltessential is the only UK retailer to stock all 365 standard colours and to display them in the same sequence as the manufacturer's colour card." They do have a fantastic range, but there were plenty that were out of stock.
I'm about to place a second order.