SNKEBIT, there are a lot of good deals for reasonable $$ on eBay. - Of course, you can get burned too. I've had quite a few projectors over the past 10 years. - Some were valued at $6-8,000. Two of the biggest factors for choosing the right one are how big you want the image to be and how dark an environment you have. Naturally, the higher the lumens rated number, the brighter the display will be. Try to get as bright as you can afford unless you're in a room that is totally dark. Resolution is also important. The larger your display is going to be the more you will notice pixelation, so go hi-res.
One of the most frequent problems is that the bulbs have only a limited lifespan. - And some replacement bulbs can run you $500. So it's worth it to check on the cost of replacement bulbs before making your choice on which projector to buy.
Another consideration is where you're going to mount the projector. Many projectors have an option to be used as a rear projector. It would mean that your projector will shine the image on a screen material that allows light to shine through. It's great for outside or if you want to drop a screen in the middle of a room from the ceiling or if you want a projector room with a wall opening that is screened.
Not all projectors have the same options for keystone correction. If you mount your projector on the ceiling or on the floor it will shoot the display at an angle and cause it to be trapezoid shaped. Keystone correction allows you to adjust the image back to a rectangular shape. Some do a better job of it than others.
The material you're going to have your display on makes a difference too. The best are specially made to reflect light more efficiently and will make your image seem clearer. At our farm we set up a theater in our barn hayloft. We had a 20 foot by 30 foot screen. IT WAS AWESOME!! Talk about a real movie theater atmosphere! I'd bought a used projector that was rated at around 20,000 lumens and also got the good display canvas. We could watch movies with quite a bit of ambient light . - Of course they looked better in a darkened environment.
For Halloween I purchase 3 different projectors. They were fairly inexpensive and we only displayed on 8 foot by 10 foot areas. That's as big as most people use. The lumens ratings were only around 2000. We had to wait until dark to see our displays.