Lots of people are liking the brand new model of the Harbor Freight 12" sliding for about $125 with coupon on sale. That is the cheapest you would ever find, but once set up right, does very well.
I have a used Rigid 12" sliding myself which can cut repeat slices off the end of a piece of wood to about 1/32" thin slices if you so desire. It is a much more expensive machine, but I found mine on craigslist used and missing a part or two and jammed up at the moment for $225. That was a good deal.
I also have a Ryobi 10" non sliding I've used for 18 years now. That I think was also $225 when I bought it then. They have gotten much lower cost since that time. Still works as good as day one and very accurate. I keep that around for outside jobs because it is fairly portable (though cast iron base).
The Rigid is in the woodshop space, never moving, because it is a monster. Ryobi also makes 10" sliding saws if you wanted. The parent company of Ryobi also is the parent of Rigid and also Milwaukee now. Ryobi also is identical to many of the Craftsmen power tools, with new cosmetics around them and makes all the Craftsmen cordless 19.2 v tools, same as the Ryobi one plus tools. Not sure about the Craftsmen 10" sliding above but may well be same as Ryobi. If you wanted to checkout remanufactured Ryobi for much lower cost, try the CPO ryobi website. They have the 10" slider there for a good price, about the same as the HF 12" slider with coupon though.
If you are new to miter saws, you have to ask yourself what you want to do with it and what is important to you. For deadly accuracy and portability, a non-sliding 10 or 12" is best. 12 of course gives you ability to cut wider boards or better do crown molding. But for not furniture building kind of construction work, you can cut wider boards on a 10" by just cutting it twice and flipping it around. The Ryobi 10" I have can cut this so the end is within about 1/32" of each half, which is "almost" square. 10" blades are also much cheaper to replace than 12" blades. 12" is less accurate than 10" because the blade will vibrate and wobble more, in general for same quality level of saw. If you want a replacement for a conventional radial arm saw, then a 10 or 12" slider is the way to go for sure, but they are heavier and not as portable and also not as accurate generally as a fixed 10 or 12", and also higher cost (except for that HF one).
Other great brands of saws to mention with various pros/cons are Dewalt, Makita, Milwaukee, Bosch, Hitatchi, Delta, even some Craftsmen (but they will be one of the ones mentioned and rebadged). I've also heard Menard's MasterForce brand has some higher quality level products that are rebadged other brands (like Craftsmen products this way) but I don't have any of those. - Paul