I came up empty handed in my appeal for info on a Model Five. What I could find is they are Guild branded Japanese practice amps, not very well thought of. The model five I was looking at had an asking price of $100, but a couple of sale records showed them going for $30-35. I would think the Model six, would be a little more, but not that much.
Solid state, not the best sound, I think you'd basically be paying for the Guild badge.
Never heard in person, but the lack of response speaks volumes. I know Grot has the series in his collection, but I bet he has them just for completeness, rather than for their value.