Spike and Merton make a good point... the punters often just think in terms of the actual playing time, but should really be thinking in terms of the total time you're away from the house - especially if a gig is going to involve significant travelling time, an awkward get-in/get-out (inaccessible venues, stairs, long corridors, no lifts, marquees in the middle of fields with no vehicle access - yes, I've seen them all!), and periods of dead time in between sets or before you start playing. So make sure you explain that all to them if they baulk at what they perceive to be a high quote.
I think the numbers being discussed are about right... £200-300 for a basic pub gig is pretty standard, £500-600 should be a minimum for a wedding/function, and £1000+ isn't unreasonable for a decent outfit and/or for a big bash. I play in bands which do all three of these types of gigs, and so my take-home wedge naturally varies from gig to gig - so I don't think it's as easy as saying that you should always be getting a set amount per gig - but as always, you'll have an idea of what constitutes an acceptable profit for the amount of effort you have to put in for the gig. I'm happy to take a smaller amount for the odd local gig (maybe midweek, or for a mate, involving minimal effort) than I would for a big wedding 300 miles away.
So basically, just make sure you try and negotiate a price that you're all happy with, and which covers all your expenses while leaving a sensible amount of profit afterwards. If you subsequently discover that another band is getting paid more for a similar gig, adjust your pitch accordingly the next time an enquiry comes in. And remember, it's easier to start high and negotiate downwards than pitch in too low and then try to get more when you realise you've under-quoted!
Oh yes, and have fun too!!!