Quoted from Whysnow:
You need to look a little harder. Taxi and ES can easily be found in the 1k range with a little hunting and effort. They will have some issues but easily found. Most Sys11 can still be found for 8-1200 if you have some patience and hunt around.
They are commonly sold for 1500plus for nice examples but when you are on a shoestring budget you can find then in need of love for under 1k.
I just paid well over $2k for my Taxi - and looked for months. Right now there are two Taxis on CL in New England - one for $2,800 and one for $2,200. A few weeks ago, member listed a player's Taxi here (in NH) for $1,500 and it sold in a matter of hours, with a waiting list to look at it. I was a few hours too late. I saw a badly beaten up Earthshaker for $1,700 - but they're rare,
This could be regional - and I have no doubt if you spent a long time looking you might find a project one in a rural location for under $1k... but you could say that about almost any title. And I'm not sure that is what the OP wants.
Prices have been changing a lot recently... System 11 - particularly Taxi, Diner, Whirlwind, Elvira and Earhtshaker - have been appreciating.