As a stupid follow-up, I was recently praming 
some of my cels and I found that, of all places, 
Wal-Mart had some nice single & double acid free 
mats of varying colors for rather cheap. Also, in 
their paper section they have acid free paper in 
a huge variety of colors (couldn't find acid-free 
tape there, but it's not that hard to find).

And as a second stupid follow up, make sure the 
art store labels your glass when they cut it ... 
the first time I bought it, they did a great 
job ... the second time, I got a piece from the 
middle of the sheet and they didn't indicate 
which side had the UV film. Took me 10 minutes of 
turning the thing over and over to figure out 
definitively which side was coated :/