I ended up finding the frost king stuff at lowes for $20 after taxes on my 3rd trip there -- the first two they had the wrong product on the shelf, and not until I found out their stock numbers did I have someone go and find it for me (on the top shelf of some random stack), fortunately that isn't not too bad and got a big roll of it.
Looks like I will be splitting my time between grainer and mcmaster to see where I get a better price on the stuff. Thanks guys!
The mcmaster stuff is 1/4'' and relatively cheap. It is what Gautum posted a while ago.
8647K23
In stock for $7.43 per ft.
Material Type: Weather-Resistant Neoprene/EPDM/SBR Foam Rubber
Shape:Sheets, Bars, and Strips
Backing:No Backing
Thickness:1/4"
Thickness Tolerance:±0.025"
Length:Cut-to-Length
Maximum Continuous Length:50'
Width:42"
Width Tolerance:±1-1/4"
Temperature Range:-40° to +200° F
Density:4-8 lbs./cu. ft.
Foam Structure:Closed Cell
Texture Type:Fine Cell
Foam Firmness:Extra Soft
Firmness, psi:2-5 (25% Deflection)
Compression Recovery:Fair
Color:Black
Finish:Textured
Tolerance:Standard
Specifications Met:American Society for Testing and Materials (ASTM), Military Specifications (MIL), Underwriters Laboratories (UL)
ASTM Specification:ASTM D1056
MIL Specification:MIL-C-3133C, MIL-STD-670B
UL Specification:UL 94HF1
Properties:Weather Resistant, Flame Resistant
Notes:Material does not have a skin.