I think the £1000 Annual cost may be a bit on the low side, but otherwise the figures seem reasonable for a 5-6 year old plane which should not have any significant airframe issues for another 10 years or so.
However let me make a more general comment. I was in the same boat in 2001. Had a budget like yours, too. The problem is that a Warrior is a low performance machine which is just about OK for general messing about but is not very good for going places. This is why sales of new Warriors and Archers have been so poor in Europe in the last 10 years that you could almost count them on your fingers. Some schools bought some but no private buyer with a brain would pay £150k for a new Warrior, or for a new Cessna 172 for that matter. These things are very bad value for money.
If I was spending £100k I would try to push up the budget a bit; for ~ £130k you can buy a 2001 TB20GT which is simply totally uncomparable to a Warrior or an Archer. This is possible largely because the prices of 4 seat IFR tourers have been bombed by Cirrus, causing the bottom to fall out of the market. And you will still be getting a plane which is cheap to run because it's nearly new. The fuel flow rate of a TB20 at 65% cruise, 138kt, is about 40 litres/hr and if you compare that with an Archer..... However the other costs will be higher: £1500-2000 Annuals for example. You will get an IFR capable tourer which will go anywhere and with a 20,000ft ceiling will get above some 95% of European weather. It will carry 4 in comfort (3 with full fuel). It will just about do UK to Prague and back without landing. The zero-fuel range is roughly Biggin Hill to Corfu. You get two doors so no climbing over the seats (and headset cables etc) to get in or out. And it has the power to get you comfortably out of a 500m tarmac runway at MTOW.
I know every pilot will rant on about his plane being the best thing since sliced bread, but I am trying to make the point that buying a nearly new traditional basic plane doesn't get you much for your money, and a little more suddenly gets you a whole lot of capability which would really future-proof your flying ambitions.