Hi
I've found you 4 nights in August here for under £300.
Upsides of the place:
It's stunning - set in woodland with a ruined stately home and a ruined martello tower, red squirrels, rabbits, and the most beautiful beach in England (sorry Holkham Bay but it is!) About 7 miles of soft white sand, great rock pools, great beach combing.
Shop that sells home made ice cream.
Also has a small but lovely playpark and a basic swimming pool, kids club disco etc in high season.
And there's a nature reserve with a bird hide and lake.
Staff are really friendly, caravans are clean, the silver one is spacious and the bronze is fine. (We go there quite a lot! :) ) If you look in lower season you can get a four night break there for £69 - even at Easter or half term.
Downside - it's really very VERY quiet there. No shops, nothing to do except play and go down to the beach - but that could be a good thing if you want to spend no money.
Tip: shop at Asda in Ashington before you arrive, as the camp shop hasn't much choice and is really expensive.