London Guildhall are in your area and they allegedly offer 'price matching' on anyone else's MCC rates. It's kind of bogus price matching though, because they only put you on a wait list and see if they can't fill it up with people who will pay full price, and then at the last minute they'll call you back and let you on board for cheap if the course still isn't full.
Their normal course price is £2250 which is £300 more than either Multiflite or 4 Forces. However the Guildhall course lasts for 10 days with a full week of ground school, compared to the other's 7 or 8 day sessions. Not sure if that means you learn anything extra or not, I'm enrolled to do it myself shortly so it might be interesting to compare notes afterwards.
4 Forces have been recently advertising MCCs at £1950, only problem is that they're miles out in the country beyond Heathrow. I'm not sure about commuting from Gatwick, however I can categorically guarantee that it's a nightmare to get out there from anywhere central in London.