I've always envisioned a Gundam-proportioned Optimus Prime instead of the boxy-looking toys from Hasbro. So when I came across this garage kit in HK, I went for it. This is a conversion kit using the frame of the MG RX-78 OYW ver.
The kit itself costs slightly over $100. The resin quality was mediocre. But at least the assembly manual came fully coloured with a pic of what your converted Optimus Prime would look like!: