Welcome to the forum!!!
Check the condition of the brakes, the fronts aint cheap! About £220 fitted for discs and pads at an independant.
Check EVERYTHING works like air con, remote locks, leccy windows, heated rear screen...... etc!
But one to look for on a '98 espace is the radio is situated in a recess in the floor on the passenger side, make sure that works as its a water trap and the often get flooded out! if you can hear tunes and the radio works, it works!!
Like any big car, look at the suspension springs that there not snapped, They aint cheap either! same with exhaust!
Other than that, like any other car take it for a good drive, try and get it into every gear.
As family cars, the insides do get a battering!
a 1998 petrol espace can only be 2.0 16v or 3.0 V6 so is hard to value without knowing what model it is... RT RTX etc etc Its the best time to BUY a car at the moment, VERY hard to sell cars just now!
3.0's are only available in auto iirc and make sure ANY autobox is working properly if its an auto! AUto boxes cost mega bucks to put right!
also check the windscreen is ok, there over £500 if you havent got windscreen cover on your insurance!
But as the only metal body panel is the bonnet, You dont really need to worry too much about rust!!!
Whats it adertised at? £££