Hi Keith,
OK, if you mean a car with seats for seven and still space for a double buggy when all the seats are in use, then your options are very, very limited. In fact, the only thing I can think of is a Chrysler Grand Voyager (or the ghastly SsangYong Rodius), but thankfully we did manage to find one of those for sale just within your budget. It’s a 2006 model on for €3,999.
If you mean a car with a big boot and where the extra seats will only occasionally be used then there are many more options. Have you considered a Fiat Multipla? Not many around, but if you find a good one they’re terrific. Six seats and a massive boot. You won’t get a Honda FR-V for that money, but you might just track down a seven-seat Honda Stream, from around 2004, for under €4k. A cracking family seven-seater, that one.
Old-shape Ford Galaxy, SEAT Alhambra and Volkswagen Sharan are all in your ballpark and all good as long as you get one that’s been well cared for and has a decent service history. Ditto the Hyundai Trajet.
Or, if you fancy something fancy, what about an early-nineties Mercedes E-Class Estate with the flip-up seats in the boot? You can fit seven people in (albeit not with luggage) and they’re rugged and built strong. Found one for sale, a 1992 2.3-litre, for €3,250. Find a friendly independent Mercedes mechanic to help you care for it and off you go…