I am going through this right now for a push graver handle I invented.
You can expect it to cost you about $5,000 for the pattent attourney. If you can't do your own cad drawings you may also have to pay someone to do those for you.
Then there is a $500 application fee when the app is sent in. There is also a fee at the end that is in the $1,200 range.
Taint cheap. Make sure you can sell the hell out of them to make it worth your while.
Ray