Good luck. You'll need it!
You can basically split pubs into two categories, clean ones and dirty ones.
The clean ones are most often part of a national chain, and will have a national franchise company clean for them. The decision and payment isn't made locally, it's made at head office. Examples are Wetherspoons, Tom Cobleigh's, Marstons, Everards etc...
The dirty ones are dirty because the landlord doesn't give two sh*ts about the state of his pub, which tells you something about the state of the average billy bunter he gets in through the door. Again, you're flogging a dead horse most of the time - even if you did get the chance to quote they'd choke at your prices.
There's likely to be a small number of free houses in your area who'd maybe be interested in cleaning work, it's just a question of doing your research. How's that for an excuse to go out and drink beer every night of the week?!
Don't waste your time with flyers! Pull up all the pubs in your area on yell.com and ring them up. Hopefully you'll get the odd little bit of interest in between getting hung up on. The holy grail is getting an agreement to go out and quote. It's a good idea to keep a record of who you call and when, and their reaction. You don't want to waste your time re-calling flat refusals.
Pricing - it's going to be a lot harder work than you think, price it well and sell it even better!