Marc, first of all, have you already paid for them? B&K seems to include the visa charge unless you ask them to drop it.
I work two blocks from the DC visa office and I decided it was still worth it to use the service. If you do it yourself it's going to cost 160-180 dollars depending on whether they charge a processing fee. Regent charges 299. So it doesn't cost that much more to use the service since they will do the legwork for you.
As far as I can tell they won't issue a visa same day unless it is an emergency. You have to come back in a week to pick it up or give them a pre paid mailer to send it back to you.
No matter which way you decide to do it you must go to the Brazil consulate website to fill out the on line application.
Also, if you decide to do it yourself check whether Arlene needs to be there too or you can submit the application for her.
Good luck. Tom.