Log in to your broker, type in BRKA and the 1 share, set it as a market order (should be default) then before your order is filled it will ask you to confirm it. On this screen it will show you exactly the current ask and bid, the ask is the price you will be paying for your share.
The stock closed today at $135,400 which you can find at yahoo finance (also includes bid and asks but with a time delay),
BRK-A: Summary for BERKSHIRE HATH HLD A - Yahoo! Finance
Hope that helps,