Best metal detector for gold coins in Pacific NW

I recently purchased the house that I was raised in and my dad was raised in. When he was about 12 yrs old they were building this house and had plowed the 5 acre field to plant potatoes. My uncle and dad seen something shiny in the field and found 12 gold coins. The neighbor boy found 8 gold coins in adjacent field and an old musket. This was about 42 years ago. The neighbors have all passed on and the other day my dad reminded me about the coins he had found as a boy. He said he had always wanted to spend some time looking but was always too busy. He is retiring and now has the time so I want to get a detector. I would like to buy a detector that is easy to run and penetrates the ground and as accurate as possible identifies gold. I would like to spend about $500. what would be the best detector for gold coins.

Thanks great site loaded with lots of information.