I don't know the exact details of the Brion Toss harness but the Black Diamond harness I have (rei.com) was about $50. It is secure and reasonably comfortable. I also made my own version of the ATN TopClimber with 2 ascenders and a harness made with 2" nylon strap. For safety I use a spare halyard and a prussick knot. I think the ascenders were about $50 each on sale.

One thing to remember when using a spare halyard as the safety back-up. If you are at the top of the mast and are somehow incapacitated your standby person has to be able to let you down. I prefer using the safety halyard as a static line. That puts my backup system in my hands, not someone elses. If the halyard is rigged as a static line with the ascender or prussick knot you need enough line to be lowered down from the deck. I attach line to the hoist end of the spare halyard and run it up to the top of the mast. Then if there is a problem there is enough free halyard to bring me down.