I use sheetrock screws. Nails are even cheaper.

gosh...I was so unclear!...wanted to find out about most economical corner type things into which you slip boards...

thanks

Typically, most people butt the edge of intersecting boards together, pre-drill holes, then fasten with coated deck screws. Corner brackets can be purchased from Lowes hardware dept., to add further rigidity.

EG

Ditto to what EG said. I butt the boards together, pre-drill and then use 3" stainless screws.

simpson strong tie makes LOTS of great hardware... corner braces, long angled pieces ,for any size, like $2 each, some coated deck screws, a whole box's hardware should be like $10... any real hardware or lowes or HD has them... takes the issue out of making 90 degree corners too....