The prices you have quoted are VERY reasonable, figuring Superior Mats is $2.50 for just the one window cut when you order 100 mats, or $5.00 per cut when you buy them each!
I've been using 4ply mount and overmat for several years now, but just this year I've switched over to using a 2ply mount and 2ply overmat. There are several reasons for this. First, I personally think it looks better! It has a cleaner, less distracting, very elegant look compared to the 4ply. Second, as my collection (and my collectors collection of my prints) grow larger, it gets very difficult to store so much mat board. By using 2ply, I can now carry twice as many prints with me when I go on the road showing work. Storing tons of matboard with prints is a great problem is todays galleries and museums because it takes up so much space. That is why I think they prefer no dry-mounted prints, because lots of places will remove the prints from the mats and store them somewhere else.
Brett Weston, Ansel Adams, and many other photographers in history have used 2ply mounts as well.
I'm a total formalist when it comes to photography, and I like things as clean and simple as possible. I really don't like the look of 8 ply mat board or images that have several windows cut around them. I feel that a strong photograph does not need such fancy and elaborate matting and framing and many people just try to make up for a poor image by doing huge fancy matting/framing jobs.
I would probably take advantage of this mat cutting service, however I find that 13x15 for 8x10 is abit small for my taste and prefer 14x17. Although Michael and Paula use 13x15 for the prints they show and sell, when they have an exhibit they mat to 16x18.
Best,
Ryan McIntosh
www.RyanMcIntosh.net