cheapest way to mount a tv?

the bracket isn't where the money goes, it's what you screw it into. on a 70s house find out what the wall actually is first. timber stud walls you screw into the studs with lag bolts (a stud finder, or knock and listen). solid masonry needs proper masonry fixings. hollow plasterboard on its own will not hold a tv, whatever the fixing packet says. a basic fixed bracket is cheap and fine if you don't need it to tilt. check the bolt pattern on the back of the tv (vesa) matches.