I guess it depends where you are getting it from. It's been recommended on this forum to take an old one to a glass supplier and ask them to copy it using appropriate glass.
Ah, well I guess it's a question of what you're happy to take for it/how long you want to wait. Sounds a bit low to me (I'd pay more for one, but then I'm not buying right now).
Don't forget older cars had toughened not laminated glass
I would pay more than 10 for a spare laminated one in fact it's worth almost as much as your insurance policy excess as these are easy to fit