Take a weekend break amigo. Catch a cheap commuter flight to Holland. EasyJet, BE, Virgin Express, BMI, etc. all have cheap ass fares for about 4 pounds + taxes each way check them out (a nice starting point:
http://www.lonelyplanetexchange.com/ ). From Schiphol catch the train to Amsterdam Centraal --buy a ticket from the yellow machine. You'll need about 3.60 in euro coins or one of their pin cards. After arrival get your ass a cheap hotel room. Do this by going to the VVV, there's one just in front of Centraal Station, but it's always packed, even in off season. A quick note on VVV in Amsterdam --you can pay for your room there with a credit card. Most places are cash only. There's another one on Leideseplein --where most of the clubs and partying goes on. To get to Leidseplein, take either the 1, 2, or 5 tram to the Leidseplein stop. The VVV is right next to the square across from the "walk to wok" Chinese take out. Also in Leidseplein is "The Bulldog" it's a coffee shop and a bigger one at that. Never been bought anything there myself as I prefer Abraxas, but that is in Spui (between Leidseplein and Dam square). You will find some kick ass weed that is a notch above the hydro that is available in Oregon and Canada. A few tokes before going to the Anne Frank House (Mrs. Pancake made me do it) last January, made it the funniest fucking thing I'd ever seen. While you're there load up on the Indonesian and the Chinese. It's all over. Indonesian is like a cross between Chinese and Indian.
If you still have a jones for Mexican food, go back to Centraal Station, get on the train that goes to Haarlem Centraal (there's two other Stations named Haarlem but neither goes into Haarlem. If you get off at the wrong one, just hop back on the next train). Walk out of the Train Station --follow the signs for the twon center to go out the correct exit, you'll see the bus station, go walk around it, on the main street that curves to the right, follow it until you get to the main square. You'll pass one Mexican Resteraunt on the right. There's another on the edge of the square that's all decked out in neon. Those, might be the two closest Mexican resteraunts to you.
In Amsterdam, skip the hookers. Most (I have my doubts about Schroeder) can drag something comparable out of one of the clubs for free.
You'll also find other Euro capital cities are much less expensive than London. Madrid is crazy cheap, Paris is fairly inexpensive as well. The only cities that I though were even close to London on the expense side is Reyjavek in Iceland, Oslo, and Stockholm. Even then Oslo and Stockholm are cheaper in the summer --fucking go figure that one.
Last AP London tip for DJ FC, if you're going to do any of the touristy shit while you're there, i.e. Tower of Londen, buy your tickets at the tube stop. The big ass line is for buying ticket not going into the exhibit. If you have tickets, just walk to the front. Also, buy you should know where to buy your tickets to Westend shows. That may be the only bargain in London. Broadway quality + shows at local community theater prices.