$65 is what a local audiologist charged me a couple of years ago. That included fitting and one set of silicone rubber plugs. I use them often and they are holding up very well. By the way I believe they are at least equivalent to a NRR 30-35 muff and they are not compromised by hats and glasses.
Gun Tests had great things to say about the Peltors. I don't think they get any better.
One thing I picked up from the acoustic doors we deal with at work is that STC / dbA scales are logarithmic. The attenuation of an STC 55 door is actually double that of an STC 50 - not a 10% increase that I would have guessed.
I'm not sure how that relates to the NRR ratings on muffs but I'd guess it's similar - if so, I wouldn't be surprised to see pricing differences apparantly out of context with dbA increases.
The "rule of thumb" I got from Riverbank Acoustical is a straightforward "bump" of 5dbA for tandem mounting of 2 similar assemblies.
stc 30 plugs + stc 30 muffs should = total performance of stc 35.