T-Slot Linear Slide question

[audball22386]

Ive been locating and designing my first machine and T-Slot aluminum extrusions seem to be the most efficient method to use. The ones i have been looking at are made by mk automation. (www.mkprofiles.com) They have their own linear slide system which is a clamp that secures two hardened rods along the t-slot. then they sell a guide roller system that are bearing that mount above the top rod and below the bottom rod. You can see what im refering to in the middle picture here (http://www.mkprofiles.com/linear_mot...ion_glides.asp)

I have a few question regarding this. MK's solution is rather expensive compared to their extrusions, so i'm looking for something more cost effective.

I also saw what 8020.net has to offer and its a slide system that surrounds the extrusion. I have seen other similiar setups, and was wondering what kind of wear and tear these bearings put on the aluminum extrusions they run on and also what type of lifespan do these bearings give before they get some sort of play in them and need replaced.

Thanks alot,
Mike

[Hobbiest]

How expensive is this design? I have seen systems like this in commercial biomed machines, and they work very well.