28 years is a long time. But, for one person to do this, in his spare time, with little or no previous experience, is some achievement. Add to this sourcing the information, raw materials, existing genuine parts, having other parts made or duplicated, learning 'on the job', the physical effort of building this, and, of course, the cost of even raw materials, such as aluminium, let alone the fantastic costs of genuine parts, then 28 years passes rather quickly.
And a 1:1 scale plastic kit for $1,000 (roughly £650) ?
No chance!
Multiply that by a minimum of x 10. The 'Gate Guardian' replicas start at around £22,000, and even if a major model manufacturer was to produce 1:1 scale kits, they'd be in the region of at least £10,000 to £15,000 if moulded in plastic, in a similar way to traditional plastic kits.