My longest taxi journey was also Indian - from the border with Pakistan (Wagah/Attari Rd) to McLeod Ganj in Himachal Pradesh. Somewhere between 250 and 300km. It was fun - the driver made quite an outing of it, brought a mate along, and we stopped for many cups of tea along the way...

Otherwise, when I was growing up in the North-East of England... I never did it myself, but it wasn't uncommon to see taxi companies advertising fares for the 300-400km journey to London Gatwick airport - a family of 4 would pay less for the cab fare than they would for the train or connecting flight. Plus, in those pre-LCC days, regional airports would often have little choice for holiday flights other than Alicante and Palma...