It sounds like you have a traditional cups-n-cones bottom bracket, and the echo indicates that the problem is indeed in the bottom bracket and not in the pedals, seat post, fork, headset, saddle, or shoe cleats. If there is no problem with the bearings themselves then it is probably a facing problem with the shell. Facing tools are beyond the budgets and expertise of most home mechanics, so your shop will need to be involved in fixing this.
An alternative would be to purchase a new sealed cartridge unit. This might be the less expensive solution.