I would think you may reach your target price level by buying privately. I bought my GTi PP privately, it was also owned by the original purchaser and not a lease car.
I prefer to meet the previous keeper to get an idea how they have treated the car, not usually something you can do at a fleet auction.
Good luck!
I was just thinking exactly the same thing when pondering what to reply to this topic.
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Many years ago after I finished college and Thatcher was making life difficult for us young 'uns who weren't born with a silver spoon in our mouth the world was a different place.
I had a saturday job when at college helping prepare cars for sale in a small garage that was very big on quality of presentation.
I went to work for them for a year or so full time learning all about the trade, which as a young petrol head who had no real interest in the electrical engineering I'd been studying for a few years it was a breath of fresh air.
This was 30 years ago and times have changed but I do still have a friend who is a manager at a leasing and hire company who does the big auctions, putting stock through there that doesn't already have trade buyers, and he will buy the odd older car if he can see a few quid in it.
Leasing companies will often have buyers lined up for tidy stock (VW UK leases more so), then there are closed auctions, auctions for this, auctions for that...
I'm far from an expert on the subject and we do have a few dealership people on here who probably won't want to add in their own comments for obvious reasons...

There is already lots of good advice on here and I can't add anything new.
If you're after a cheap Urano Grey Passat with a few miles on it you'll easily pick up a cheapie at auction on a good day. If you want a cheap base model Focus or Citroen or something along those lines then you will be in luck with a bit of patience and quick reflexes.
The trouble is with GTI's they'll be quite sought after by the trade as not only will big dealer groups take the volume of stock, but there won't be a huge amount in the system unless there's a big lease promotion that's come to an end of the 24 month period and they've been dumped into the open market as main dealers are flooded with them.
GTI's of a certain age will be less common at auction as VW UK try and keep as many as possible under their umbrella so they can manage trade prices and their finance on them.
That means cockney w*nker traders, wide boy dealers and small garages who can smell a car that won't be sat on their forecourt for months will be your competition, not to mention any private hopefuls like yourself who have the time and energy to go through that system of buying. it's all good high octane fun but you'll easily find yourself outbid on nice stock or even worse find yourself overbidding.
What are your standards like Matt 17th December 1991? Be honest with yourself. Do you want a car you can get back to mint at minimal cost or are you the sort of person that is quite happy for an average condition car? That does make a big difference, the people i know who pick up auction bargains have quite low standards of what they'd accept as they treat their cars like workhorses, they let their kids strew crap all over the inside of it, there'll be loose change and charger cables sat on the seats and carpets, drink cartons in the footwells, happy meal toys thrown around the place etc. If you're happy with the latter then you'll get what you want at auction. If you're a fuss arse like me who likes people to wipe their shoes off before they get in, if you lose sleep over a tiny stone chip or sulk for weeks if you get a tiny dint in the door panel then you'll be very lucky to pick up something that doesn't require some signicicant expenditure. Most people are probably somewhere in the middle of those two extremes, hopefully you are too.
Factor in the cost of a warranty too, you may well pay quite a bit more at a dealers but you'll get £500 worth of warranty on it if it's 3 years old on top of the fact they'll do all of the small bits of work on it that will be bugging you.
As Clubsport says, if you want a mint condition car to start with and will really look after it well then your money would be better invested in a private purchase which will be in between the two prices.
Wanted ad's on forums can turn up some nice cars if you're patient. You'll likely get a few chancers reply but if you time it right you'll find people with well looked after cars who find part ex prices insulting or are buying from a broker that don't offer top book money in part ex like a main dealer would for a mint car if there was still enough money in the deal for them.
Factor in what you'll pay at auction as a private buyer over what some guy with a performance car garage in Leicester will bid, plus a bit of tidying of the auction car, sorting out dints, getting alloys refurbished etc, removing two years of Eastern European car wash paint defects versus buying a tidy one off a realistic private seller...
CAP set their prices at what the trade can pick up cars in auction for then spend xx amount getting them prepared for retail and then priced so that they won't sit on a forecourt with no interest for months on end. So those prices are realistic but not the be all and end all- what they are though is a very good indicator of the true worth of a car in an open market. Once you get into older cars and enthusiast markets there is a gulf between the two that opens up depending on condition and provenance.