I worked in an engineering group that specialized in automation. You get what you pay for basically. so with us hobbyists, we live with what we can afford. Oh and always buy your bearings and rails as a set from the same manufacturer. Do you need the precision of a $200 rails? My opinion, no. But I dont need the 435hp my 5.0 puts out but its nice to have.. and therefore wont argue against you.
Misumi I believe will let you buy direct if you register with them. I dont think there is a min order either. We got quite a bit of rail/bearings and extrusion from them in the past. I would check ebay for brand names NOS parts etc.. Also, I dont know the design well enough on the ft5. can you add any side preload to take out the "loose" feel?
There is another way, where you loosen one rail, and you have these essentric screws next to the rail, in at least 2 places. You tighten down these screws and it puts a side load on the rail/bearing assy then tighten down the profile rail...