We used the Weatherly plans for this project amending in a couple of places. The two seat version was attached to the three with using just one set of legs and then we added a 2 x 6" upright at the join and put another 2 x 6" on top for a drinks tray! Rather than 8 individual 24" cushions we went with 48 x 24" seats and did the same for the backs.
The cost for materials was only about $70 and the outdoor fabric was twice that amount. As it is under a covered deck we just used 4" foam for the seats and 2" foam for the backrests, costing about $100. All Canadian Dollars.