Depends on what you're getting but probably in the 8-9 range for First Class. Both of the below are under $2 in the US.
First Class Small Package 3oz (seals or misc) (more than 1/4" so has to go "package") - $7.65
First Class Small Package 6oz (Valve tool) (more than 1/4" so has to go "package") - $8.80
I will say that while they might have only charged you $10, it cost them more than that even for first class. I'd have to weigh a PGP again but they're not light. I guessed 2 or 3 lbs packaged and the current rates for that are below.
First Class 2 lbs - $16.55
Priority 2 lbs - $31.60
First Class 3 lbs - $22.15
Priority 3 lbs - $33.55
I usually ship PGPs in medium flat rate boxes. I had one guy who wanted me to use a small flat rate but I don't think there's any way in hell to fit one in there even disassembled and there wouldn't be much padding. These are the current rates for flat rate priority mail. Yes that's ~$12 for US and ~$42 for canada.
to US Priority Flat Rate
to Canada Priority Flat Rate
Anyway, I'm just tossing out the reality of it. The rates were *much* cheaper even a year ago. They've gone crazy.