Sovereigns

[Phooey]

Hi, after a little advice please. My father has asked me if i can find out how much roughly a full, AND a half sovereign coin is worth. I presume he means roughly how much would a dealer offer for these coins. He also wanted to know how much a 1904 20$ Gold coin is worth, so i had a look around ebay and found a few in the £800-£900 bracket - does this sound about right?
Unfortunately i do not have any more details i.e. type and date at present.

Cheers