I've always fancied busking. If you're really good, obviously totally dependant on factors of footfall, location, weather, time of day / night - I reckon a good solo or duo can gross Β£3 a minute (Β£180 per hour), and that's with a setup no more sophisticated than the 'big issue' lady...
If you're a band, with some trustworthy mates as bucket persons, playing off a flatbed truck in a pub carpark or near a campus, burger van etc - Β£300+ an hour?
Elvis Costello in disguise, with just an acoustic, a fishing stool and an upturned hat would gross Β£300 per hour, easy, I reckon.