I second the TB20 but I don't think all have 5 seats officially. Mine is a 2002 TB20GT and there are just 2 seat belts in the back.
Reportedly some U.S. owners have removed the middle seat belt because it saves on insurance premiums (fewer passenger seats).
Otherwise, the TB20 is a great plane, the best of the lot of you want something "nice" and very capable.
However, for long legs (I don't mean womens' legs) you need to consider the creature comfort. A 5-seater will have no room to move about if you have 5 crammed in there. I fly many 5+ hour legs with my girlfriend and she often likes to climb in the back seat and have a sleep, or make some food, or just have a stretch. Or use the "loo" (the plastic bottle thingy) with some dignity. Anyway, with survival gear (a raft, a bag with some stuff like a GPS and a radio/EPIRB) that's one seat gone.
One ends up with a much bigger and much more expensive to operate plane...
Re operating cost, this depends much on age. An aluminium airframe should cost next to nothing for the first 15 years or so, assuming it has not been maintained by apes (quite an assumption especially if you take it to big JAR/EASA maint companies). So it's a tradeoff between a new/newish plane and low maint costs, and an old one with less spent up front but lots and lots spent regularly afterwards.
Euro 100k might buy a right old heap. Any IFR 4/5 seater for Euro 100k is going to be in a state. A good TB20 is 2x that.