I think you're going to struggle to get anything decent with that spec. for £100. Most around that price appear to be 24L, 7CFM. They aren't rated for anything like 100% duty cycle, either, and will overheat if you let the motor run continuously, so you'll need to plan for some breaks in your work both to let the air recharge and to allow the motor to cool. As such, you probably need to go a size or two bigger than you need on paper. I wouldn't be surprised if the CFM specs are optimistic either.
That said, the Ebay compressors all look basically the same as the Clarke / Airmaster ones that Machine Mart sell. I think they're probably all the same Chinese-sourced stuff branded differently. If that's the case I have one of the 7CFM 24L ones that's done me fine for probably 5 years or more now. Only used for tyre inflation and the odd use of a couple of air tools.
Some of them are oil free, which might be a good idea for spraying, not that I've ever done it myself.