For $600 (or less!) consider buying a welder and using a tilting or drop down design. Simple enough to build and you get the feature you need, a welder, and the future opportunity to be creative.
This isn't mine and I would do it similarly, but this design is much simpler with fewer moving parts than the tembo tusk and engel versions which i hear are prone to eventual failure.
I built a sliding fridge mount for about $40 in material and 3 hours of work and bolted it directly to the floor. Since I had limited time availability, I didn't get many pics... but here's one as I was welding it together.
In my vehicle, I use the area above my fridge to store dry food stuffs in cheapo plastic boxes. Keep in mind I designed and built the temporary solution below a week before a trip...
My justification is that the dry foods are lighter weight than the fridge and putting the fridge atop a drawer system complicates things further. I'll be designing a modular system with a singular drawer to the right of the fridge with a similar style shelf over the fridge. I'll be putting an air compressor the left of the fridge (efficient use of space). In the drawer would go tools, spares, and recovery items. Atop will be the rest of the gear that resides inside the truck.