Just do it. Detecting for coins, jewelery etc. is a strange hobby- it doesn't depend on equipment so much as location & local knowledge. So you can get into the game for about $70 or so, and recoup your money in a short time if you're lucky. Start in your backyard, and go from there... beaches, parks, old ruins, vacant lots... just amazing what you can find.
You do have to be a little bit mad to enjoy it though...