FGAS (Flash GAS]
A Sunpak G4500, 4205G and 455. I received the first and last of those yesterday for £16 (incl postage). Those two are identical, the G4500 being called the Auto 455 in North America for some reason and IDK how this one got to the UK. They were on Ebay "from a house clearance" and sold "untested" but they both work fine. They have a few rub marks on them and one lacks its battery holder.
I got the G4205 (544 in North America) some months ago for £12 including postage and it is in mint condition. Slightly lower Guide Number (42 rather than 45) but has some advantages over the others. For one thing, the model name on the front is nicely moulded in the plastic, but the G4500/455 have sticky labels, which are deteriorating and look tacky.
None of these have any camera dedication and are fired via the camera X connection - suits me. All the trigger voltages are low and I've been using them on my K-1.
So I paid an average of less than £10 for each of these. I have just bought
another G4500 from Ebay, non-working, to get the battery holder and possibly to mix-and-match parts to get the best of everything. I shall keep the 4205G and the best G4500/455, and re-sell the rest.
PS: I have already put reviews of these in the PF Review section.