how much would it cost for somone to install a new rear seat belt on an ef sedan. its to hot outside today

I just put one in my EL wagon(same Part number) Repco had them on special for $70
It's a 15 minute job to change, only thing you need is a torque set socket (about $20)to undo some of the mount bolts.
Probally take longer to drive to Repco to buy one than fit it.

torx bolts hold them in, its size is T50.i bought a single one for doing that job, cost $3.50 from local parts shop