For a mini in reasonable condition and little rust i'd be guessing maybe 4000 for a fairly standard colour in 2pac. Once you start going fancy with metallics, pearls etc the paint itself can get very pricey, like between 500-1000 for just some colour, then clear coat on top of that. Most of their costs is labour, they need to see the car to see what panels need to be straightened, if rust needs to be cut out and new panels welded in, they just don;t know what surprises they might find without seeing the car. Cause if they say over the phone that it might cost around X$$ and when the see the car it really needs a hell of alot more work, then the owner might try and stiff them buy keeping them to their original quote or the customer gets angry cause it will cost them heaps more to paint. There aren't too many paint shops who will just paint your car though nowadays for variuos reasons. they either do the whole lot, or nothing. Theres stories of people bringing there car in to have just the colour put on and then when 6 months down the track the paint start flaking off, the customer tries and blames the painter when it was their own bad prep that caused it and so the painter ends up having to refund them anyway.
You can always save yourself a hell of alot of money and do it yourself in acrylic
Cheers
Ash