If you've seen the PJ you like and the price is within your range then buy it now, if you wait for the price to drop do you then wait for it to drop again and so on......
I see Pixmania have a £30 off xmas offer and the Epson TW5900 is £912 right now which is a good price,Pixmania have mixed reviews though.
I am sure there will be other offers about as we get closer to xmas and sales do not pick up.However don't expect to see big reductions 10% max on the newer models maybe a bit more on older stuff.
The things is as TR has said buy this side of xmas so you can use it over the holidays and enjoy it while you have time off.
tesco is very good on price and i believe you can just bring it back a week later if you change your mind if its all ok etc. got to be less fuss then sending it by post etc.?
I am no expert, but have just bought a warrantee return HD20 from Optoma for the bottom end of your budget. It looks brand new. If you are interested in on call Richard on 01923 691858, he was very helpful & nice to deal with.