A: Call your local HD and ask for the lumber department or Pro Desk and ask what the price is. Also ask them how many are in stock. if they are low they will allow you to pay for them via the phone to reserve them for you. Good luck with your project
A: Call your local HD store and ask for the Pro Desk. They will be able to answer your questions.
A: You can cut a lap joint, drill a 1/2 or 3/8 diameter hole in the center of each end and drive a piece of rebar into the holes. in your HD store in the lumber department you can buy a splice place pound it into the timbers and then screw it into the timbers to aide in securing them ( place the splice plate on the dirt side or down so that it can not be seen.
A: If it were me, I would join them with a 12" piece cut from a timber & bury the joining piece, nail them while leaving the 8' sections lie on the surface. You want to drill holes near the joining piece and drive in rebar, sold at HD, to secure the timbers. See picture. This is done stacked two high but the idea is the same.