Holiday cottage in August for < £450 within driving distance from London

[johnnybuoy]

We're looking to go away for a week in August to a cottage somewhere within 4 hours drive of London that must be within 15 mins drive of a sandy beach.
We need 2 rooms as we have 2 small children. It doesn't have to be fancy as long as it's clean.
Ideally would go to the West Country but it seems to be so expensive.
Any suggestions greatly appreciated?

Have a look on ebay if you can wait until the last munute. We are off on Friday for a week in Cornwall that cost us £300 usually £750.
for example might take an offer
keep your eyes open. this site is good too.

Thanks, I'd never have thought to look on Ebay!