Hi,
Nigel, i was going to suggest a home brewed model too
I built my own and it's robotic so it tilts back and forth.
It's possible, but you have to be very careful to make sure it
is extremely overbuilt so that it is sturdy because you dont want it
to fall during earthquakes or after many days of normal vibration.
The trick with mine was finding the right screw size for the back.
Once i found that it was just a matter of good construction technique.
To really play it safe you can include a beam or two that reaches all
the way to the floor that can take some of the load, rather than the
wall taking all the load. Paint it, make it look nice, build some shelves
under it, and you have a whole custom entertainment system unit.
Maybe stain the wood instead for a nice finished wood look.
You can sure do a lot with 500 dollars and certainly get a lot more
than a single wall mount with that much money. I bet it can be
done for 50 bucks, but 200 will get you a really nice looking setup.