£600 will get you a quality (Advan etc) set of second hand rims with tyres if you're patient and watch the for sales like a hawk bud, especially if they're in need of a refurb. Keron's got a set of racing hart's in 19" for around that price at the minute, I'll have a look for the link.
£100 will cover blasting and powdercoating (I've the number and address of a place near Donaghadee that will do it for this price) in black, but on a white car you'd probably be better off going for black centres with a polished lip.
You could be lucky and get a bargain, I bought a set of 18x9 and 18x10 split rims for £180 in Larne last week, they're currently with the powder coaters
Edit: link to Keron's for sale thread, looks like someone's taken the Hart's
https://www.mkivsupra.net/vbb/showthread.php?t=204757