I bought a Whirlpool for Lowe's 5 years ago for $500. Paid them and additional $199 for the install. If you are replacing one then you can do the install yourself. If it's new, like mine, then $199 isn't bad. You can pay upwards of $2-$3k for a Culligan or Kinetico but my Whirlpool does just fine. Not sure if there would be a discernible difference in the quality or lifetime. I figure if I need to replace mine every 5-7 years, I'll still come out ahead.
I recommend the self install if you have an existing unit, WAY cheaper than Culligan, Kinetico etc...
Lowes charge of 199 is not bad for a new install.
I have replaced 2 units so far in two houses and it was pretty easy. Just some minor plumbing, the 1st unit is on year 15 so probably about due for replacement. Oh it is a GE that I bought at Lowes