RS....the mayor of London has decreed that black cabs cannot be older than 16 years old to qualify for a hackney licence meaning there are a fair few well cared for teenage black cabs out there looking for a new home, fleabay/loot/exchange and mart and the london/home counties car auctions would be my first port of call.
Was looking to buy one myself recently to replace other halfs 200000 mile + astra....she veto'd it

the one i was looking at was 18yrs old with full service history really tidy full mot £1195
this was the cheapest i found after a quick trawl eBay item number:
151117493585
i'd hang on and pay a bit more for a tidier one but it gives you an idea
a bit dearer and more modern eBay item number:
171072039105