You really need to consider what type of waterproofing you are going to use in your shower as that can point towards using a particular drain. not all are compatible with a liner and a clamping ring. More of them are designed for a surface applied sheet membrane (such as Kerdi, or Hydroban sheet, or Noble). Personally, I'd seriously look into using a sheet membrane for waterproofing as it makes the thing somewhat simpler in the pan...only one layer of mud needed.
Often, the drain is sold as two parts: the base and the grate or cover. Often, your least expensive cover is one designed to use tile verses a metal one. One reason why the grates and drains are expensive is it's tricky to get something that long, relatively light-weight that is nice and straight without warps, bends, or curves.
If you haven't looked at a sheet membrane, check out the videos from
www.schluter.com. They have the most. The other, similar products are just that, similar, so those will give you a good idea of the technique.
Having the entire interior of a shower waterproof verses just the pan has some significant advantages IMHO. Neither tile nor grout is the waterproofing in a shower. It should not leak, if used, before the tile is installed. Making it waterproof also means it dries out quicker, making it harder for mildew to form.
