JT Sprockets and DID chains is what you want, X-ring if you can, but O-ring is fine too. 15 teeth on the front sprocket, 47 on the rear sprocket and you need a 118 link 525 chain. If you find a longer chain for cheaper then buy it, it can easily be shortened. Go for the gold looking chains, they don't corrode.
It's not a full hour's work to change a chain on a Wee, assuming you have a proper chain breaker and riveting tool. £80 is very steep, IMHO, find a local independent with good reputation and you'll let them do it.