If you don't want to do water parks or hop between parks then a basic 6 day MYW ticket would be the cheapest.
Undercover tourist have some at $260
http://www.undercovertourist.com/orlando/attractions/magic-kingdom.html#89
Works out at £162.
If you wanted water parks, Disney Quest, hop between parks or think you might want more than 6 days consider a 14 day Ultimate at around £220pp
Link to popular sellers here but prices need updating
http://www.disboards.com/showthread.php?t=2726040
4 days with Uni/IOA best ticket would be the 14 day unlimited around £86
1 day at Seaworld direct with their website, $8 off for a 1 day ticket with 2nd day free
http://www.seaworld.com/Tickets/Visitors.aspx $72 + tax. If you wanted to do Busch also then for £73 you can get a 14 day unlimited ticket for both parks(also includes Aquatica free just now)