Hi Steve
Have a look at the buyers guide that I linked to in my reply to you on the New Members message board, the links down the l.h. side of the guide will provide a step by step list of things to look out for which you could print off or just write a few notes to remind yourself.
Avondale sadly went out of business a couple of years back so replacement panels might be difficult to come by but most interior fittings are still available.
If the sale is private the transaction is effectively 'sold as seen' so it's vital to inspect the caravan thoroughly before parting with your hard earned cash.
First, silly though it may seem, ensure that the person selling the caravan has the right to sell it, proof of ownership could include bills, receipts, documents etc. Make sure that you go into the vendors house, don't do business on car parks or motorway service areas.
A full service history is desirable, in reality for a 13 year old caravan this may be asking a lot but proof of regular maintenance is a must even it the owner carried out work himself and provides receipts for parts etc.
Damp is the biggest killer of caravans so evidence of recent damp testing would be a good selling point, if there is no service history, no evidence of regular maintenance and no recent damp test the asking price is way too high and personally I'd ask the vendor to have the caravan serviced by an approved caravan engineer (an approved mobile engineer would be less expensive) who would carry out gas and electric safety checks, service the hitch, brakes and test for evidence of water ingress which would lead to damp.
In common with some other manufacturers at the time Avondales were sometimes prone to end panel cracking.
The GRP front and rear end panels in some cases developed small cracks, particularly at corners close to the roofline, if there is any evidence of cracking then no matter how good the caravan interior looks - walk away!
Don't be afraid to look inside cupboards and underneath bed lockers (take a torch) ,lift cushions and if scented candles or air freshener blocks are in evidence be prepared to find some damp which often gives off a musty smell which vendors attempt to disguise.
Look behind curtains and on curtain linings for signs of black mould which is indicative of damp, slightly lift window rubbers and check wallboards for bumps or soft spots.
If all is well ask to see the water pump fridge, gas fire and water heater working and chheck that there is a spare wheel which on Avondales if I remember right were inside the caravan underneath a floor panel.
Check the exterior, look for water inside light covers (damp), cracked mastic sealant, loose grab handles and overall condition.
Budget for a set of tyres, although there may be plenty of tread left on the tyres the sidewalls deteriorate over time and tyres over 7 years old should be replaced.
Ask about accessories, an ehu lead, leisure battery, step, aquaroll and waste hog would be useful and if there is a good awning as part of the deal better still.
It's always pleasant and exciting when viewing a potential first caravan but keep a level head, do the checks and be prepared to haggle.
There are loads of suitable good used caravans within your budget, so don't accept second best or excuses and you will end up with a good solid caravan that will provide years of enjoyment.
Good Luck and let us know how you get on