Hi, Welcome to the FCF
Your £1000 will get you into a very nice C5, if you look hard enough.
As always diesels are more expensive than the petrols so if your mileage isn't huge then I would go for a petrol, as this will get you a bit later, lower mileage and hopefully tidier car. However the diesels do the miles very well and the interiors hold up nicely to wear too.
I have just spotted
this Exclusive on autotrader. Its an auto 2.0 16v (I actually thin a C5 would suit an auto box well) and it looks superb, almost immaculate and its low mileage plus it has the optional leather and satnav - looks like your looking for a high spec going by your other posts.
Try and avoid the earlier ones if you can, Y and 51. The earlier cars are always the ones with the most problems, hopefully these will have been ironed by now but there were revisions during 2002 which make those the better ones to go for.
By this time their suspension spheres will be getting tired and giving a bouncy ride, so bounce the front and rear of the car and see if you think its soft or bouncy. Yes the suspension should go up and down though this is the least of the checks, its suppleness is what to check, along with trying to spot any obvious leaks. Check in the LDS tank to see if its fluid level is where it should be. Generally the C5s suspension system is very reliable and the spheres last a good long time.
I guess you have done a bit of reading up on them now, there is a very good source of info on here if you search or C5 buying advice.
I find C5s very reliable and I really like them, I wouldn't swap mine for anything else.
Good luck with your search for a C5, they are about in big numbers so finding a good one should not be too hard.
Some others I came across which look nice:
2002 CITROEN C5 2.0 HDi 110 LX
2001 CITROEN C5 2.2 HDi SX
2001 CITROEN C5 2.0i 16V Exclusive 5dr Auto Hatchback
2001 CITROEN C5 1.8i 16V SX 5dr Hatchback
Of course if your mileage is very low, there are plenty of V6s within your budget ...