You'd be talking around $30-50 per pair rather than the $21 you're being charged. If you want soft close, put it in now and save your time, money and aggravation of a DIY job.

http://www.rockler.com/c/drawer-hardware.cfm

But they are NOT cheap. You would pay more than $21 for the slides, and then have the hassle of retrofitting.

As others have said, it's generally more cost and time effective to have soft-close included with your cabinet order. The "soft-close" feature is part of the glides themselves so if you tried to DIY, you'd have to replace all the drawer glides...time and labor intensive since glide installation has to be precise. Glides are not inexpensive either, especially if you get the better glides (strongly recommended, especially for wide drawers, drawers that will hold heavy things like glass, pots & pans, dishes, etc., and drawers with only one drawer pull).

Doors, now, are a different story. Those you can usually DIY yourself for a lot less and with little effort. IIRC, our KD/cabinetmaker wanted $50 per door for soft-close. We purchased the dampers for less than $4 each...for a total of around $80 for 18 (including $10 S&H). Installation of all 18 was easy and took somewhere around an hour. Definitely worth doing DIY! (We got them online at Woodworker's Hardware in 2008.)

Great insights. Thanks so much for taking your time to respond. We will get the upgrade with our order then. Yes, for soft close door, we can definitely DIY.

Most of my cabinet companies install the soft close door bumber in the factory for about $6-8 each and my mark ups are 35-50%. A lot of the $4 soft close guides on the internet are not as smooth as the unit used by most mainstream manufacturers. I keep a box of the aftermarket units around for some one who wants them on cabinets that are not offerred that way from the factory. Mostly entry level products. They cost me $2 each I have to buy a box of 100 at a time and get them from one of my cabinet companies. You can not install them at the right spot after the fact either. You are not able to pre drill a pilot hole at the inside corner of the cabinet opening. If you install the screw there it will split the wood. So you end up installing the device in the middle of the cabinet door instead of in an inside corner like a factory installed unit.

Drawer glides are not that easy to do after the fact. No one has yet to point out that most cabinets that are not soft close under mount drawers are side mounted epoxy glides that you would remove and have all the holes to fill with something to make them not look terrible. Your new glides may not mount to the cabinet in the back at the same height and horizontal location. Most cabinet companies use as pre drilled hole system to snap in the back peice that lines up the glide. If the configuration is different you will have a nightmare to deal with while you have limited access to the back of the cabinet with the countertop on. You will have to notch and dril holes in the back of the drawer box also. Get any of these things wrong and your drawers will not be level they many not extend out levely making the drawers rub against each other or bang together if you have drawer bases etc.

It is not worth it.