There are many older L lenses for less than $1K. The 80-200/2.8L, 28-80/2.8-4L and a few others come to mind. I purchased my 200/2.8L for less than $1K.
As for the MP-E 65, it's a dedicated manual focus macro lens capable of 5x magnification. It is an EF mount lens, and fits all EOS cameras.
Canon lenses can be roughly divided into a few categories :
1. Low end kit lenses: Lenses like the 35-80 or 38-76 zooms which come along with low end bodies like the EOS-88/66/500. These typically have plastic lens mounts and a micromotor AF mechanism.
2. High end consumer lenses like the 28-135 or 28-105 zoom, and some primes like the 24/2.8, 35/2 etc. These are typically more well built, have a steel lens mount, and usually have a USM motor for fast, silent focusing. They usually have a distance scale too.
3. High end (professional) L lenses. These typically have very sturdy construction, USM motors, and wide apertures (70-200 f/2.8 etc). They are the ones priced in 4-digits. These usually come with a lens hood, carrying case and a tripod collar for long lenses. They also have a red ring.
Canon AF motors can be classified as follows:
1. MM : Micromotor. This is the cheapest motor used. It's typically found in low end lenses like cheap kit zooms and some primes like the 100/2.8 non-USM and the 50/1.8-II. Its focusing speed is slow, but on some lenses like the light weight 50/1.8-II it can be quite fast due to the small amount of glass it has to move. Putting it on the 100/2.8 macro was a disaster.
2. AFD : Arc Form Drive : This was popular at one time. Most old Canon lenses use AFD. Some current lenses like the 24/2.8 and 35/2 are also AFD. They are noisy, but usually fast.
3. Micro-USM : This is a cheap variant of the ultrasonic motor. It's found in some mid range lenses like the 75-300 IS, 50/1.4 USM etc. It is quite silent but does not allow full time manual focusing (turn the MF ring to focus even while in AF mode) except on the 50/1.4.
4. Ring-USM (the king) : This is found in most recent Canon lenses like the 28-105 and 28-135 zooms, and almost all L lenses. It is very fast and silent. It allows FTM (full time manual focusing).
Other notes: Variants in lens naming (mark-I, II etc) are just to identify later versions of the lens.
Hope this helps.