Just did a quick search @BresciaBike and Economy Classic with Virgin, travelling out on 13 October from London would be £675.39. but beware, the day you travel massively affects the price for some reason - if you went on 22 October it becomes £803.39 
And as high season starts in November, then prices increase even more then, so if you could travel in October, that would be better value.
(Appreciate you'd have to add in the cost of getting to London or Manchester.)
We had an AirBnB on the West coast, near Holetown, which cost us £579 for 7 nights. That was a small, one bedroomed condo but also with access to a private beach club and pool, so it was terrific value for money.
Eating out can be very expensive - but doesn't have to be, and there are loads of places to eat good food relatively cheaply.
It's a small island, so getting around is pretty easy - buses cost $3.50 (Barbados dollars) which ever bus you get/wherever you go, which is around £1.40. We hired a car for a couple of days, which was expensive - but it was delivered to our condo and picked up from us as well, so I'm guessing that added a premium. But there are loads of car rental companies - as well as loads of people/companies who do island tours if you want to see more of the island but don't want to drive.
All beaches in Barbados are public, and most/many have loungers and umbrellas that you can hire for the day - cost depends on which beach, but we generally paid $30-40 (Barbados).
In terms of 'enjoying yourself' that depends entirely what you want to do/what you mean by 'enjoyment'! The South Coast, around The Gap, is much more lively than the West Coast.