ok to make the buyable weapon thing select a gun and spawn it and lift move it to player height and set its name to whatever the weapon is and set the constraint flag on.
next create the entity point_template and set it like this:
Name : something
Template : the weapon name
Then go to the weapon and set a output on player pickup to the template to force spawn and maybe set the delay on.
next create a point_clientcommand and set it like this:
Name : command
next create a trigger (if you dont know how to do this then well ........) and set a output on tirgger to the client command and set the parameter to for example : sv_text M3 Shotgun 1200 Points be careful as its only allowed 4 separate words and are not allowed to use "" as it messes up the map vmf file.