The standard 5spd is the same as the box used in the 2850 VH. Wasn't used with 3.3 in the VH as it supposedly couldn't handle the extra torque. Surprise, VK 3.3 with the same box.
Here in Perth wreckers charge anything from $150 - $600 for them as they claim they are very rare. A 4 spd M21 is from $100 and up.
If you have the room for another car (looks like you have a big shed) you could buy a complete unlicensed manual for as little $100 but probably closer to $500 and of course you would have the box but also all the other bits like pedals etc and then the rest of the car to resell or use for parts. You could wreck the second car and sell the auto seperately and possibly get the money you spent on it back.
This is based on what I see here in Perth so may differ where you are. I have seen crazy prices (to WA residents) asked for wrecks in Melb & Syd.
Also buy a new clutch kit, don't mess around with a used unit.
There are many boxes you can get to fit but the prices are much higher, Sillycar, sorry Celica boxes etc but they are stronger.