At £85 I'd say you're not being ripped for two colour and the stuff you are having done - not the cheapest, but not ripped.
With regard to colour, this is where you have the problem. Anything other than the colour you want is not the colour you want (if you get my meaning). Sure it may look good, but if you stand it next to a bike with the right colour, you might be disappointed. If you insist on having RAL 5005, your man can get it, I'm sure it'll be no problem, but you'll probably find the price goes up (and by quite a bit). This is because he'll have to order a box of powder he may never use again (unlikely that it'll never be used again, but that's business for you).
At the end of the day we all come up against these issues every now and then. Did he show you the colour he's going to do instead of RAL 5005?