Even self spray isnt cheap
£6+ a can, and you need AT LEAST 4 cans.
Primer, probably 2 colour, and a clear coat.
I tried (and failed) to do this well, so tbh, dont bother until youve had a bit of practice.
Or find a local sprayer, slip thme a few notes, and ask them if when they're next doing black they can let you know, they'll probably waste more than it takes to do the case in overspray etc Probably less than £50 if you find the right garage, and will be a MUCH better job, unless you know what you're doing.