Price field with Currency outside of commerce and ubercart
I'd go with Commerce Price (part of Commerce). You don't need to enable the rest of Commerce.
The price module itself is relatively small (while giving you price calculation, and Rules integration for free, if you need it), and the rest of Commerce won't be loaded, taking only space on your hard drive, which probably doesn't concern you much.

That's the beauty of Commerce separation, you can use only a few modules that give you exactly what you need. I've seen that happen in many projects.