Whats a reasonable AC at 10th level?

[Nail]

We don't fight every all encounters we meet, so approximately 1 per 1½ hour.

That's about what we do in our group. Maybe 1 combat every 2 hours of play time. I'd call that "a moderate number of encounters".

If we're looking at your PC's AC, the first place to go is magic items. I'll be conservative here:

Given you are a Rgr 9 (average wealth 66,000 gp), you'll want a Mithril Breastplate +2 (8200 gp), some item of Natural Armor + 1 (2000gp -- I prefer Bracers), Gloves of Dexterity +2 (4000gp), and a Ring of Deflection +1 (2000gp). That's a total of +8 to your AC, plus whatever Dex you have, and you've only spent 16,200gp, or 25% of your wealth. Given that Dex is your Rgr's schtick, you'd be well served by increasing those Gloves to +4 Dex, etc.