I'm not familiar with that specific model; however, a search on Google turns up two recently-ended Beseler 45 enlarger sales. One sold for $255 and the other reached a high bid of $112.50 but didn't sell because that was below the reserve price. Neither was the MCR model.
As to the difference between a cold head and a compressor, I've never heard the word "compressor" in reference to enlargers. I think you mean the difference between a cold head and a condenser. These two things aren't really mutually exclusive, although I believe that cold heads can be used without either a condenser or diffusion configuration (see below). A "cold head" is basically an enlarger head with a fluorescent light source. Such heads are generally used on large format enlargers; few medium format and smaller enlargers use cold light sources. This contrasts with other light sources, such as tungsten or halogen bulbs. My understanding is that cold heads are good for B&W work but not for color, even with the addition of color filters, but I'm not positive of that. I'm not an expert on cold heads, so I'll leave it to others to describe their pluses and minuses in more detail.
A condenser head uses condensers, which are similar to lenses, to spread the light evenly over the negative. This contrasts with a diffusion design, in which the light is bounced around a box to even it out before it hits the negative. Condenser enlargers have a reputation for producing slightly sharper and contrastier prints than diffusion enlargers, but at the cost of scratches and dust standing out more in the print. Some people get quite emotional about the benefits of one or the other. If you're just starting out, I wouldn't worry too much about it; both systems work, and it's hard to say which one you'd end up preferring if you could spend time with both. The large area of cold head light sources, which are often formed in bent tubes, will affect how a condenser or diffusion box is designed to work with them (vs. a tungsten or halogen bulb, which is closer to a point source of light).