How much would a 1906 silver US quarter be worth?

At 2010 values a US 1906 "Barber" Quarter in regular circulated condition (Good-Very Good) will be worth $7 for any mint.

Further values: Fine-F, Very Fine-VF, Extra Fine-EF, About Unc-AU, Uncirculated-UNC

"P" Mint (lacks a mint mark) $20F, $35VF, $70EF, $115AU, $200-325 UNC

D Mint $25F, $40VF, $70EF, $145AU, $225-450 UNC

O Mint $40F, $60VF, $100EF, $200AU, $300-550 UNC