The best I've seen is $2500 for a Diplomat! (I know, not a 45, but still!)
If you trawl Gumtree or Facebook market place (eeeesh) you can very, very occasionally see some for less than $100 that are a good buy. But they go really quickly. It'll be great when the flippers flip off.
KenW, nice couple of mowers you have there. Are they RATO powered? Are they essentially GX100 knockoffs? They look very similar but I can spot some differences. I'm keen to get something new that is close to the original Kirby form factor that bolts right on, but it looks like you've needed spacers to lift the motor up? Sorry to send this a bit off topic...
If you follow the online sales of mowers, you can get familiar with the mowers and watch when someone has bought one for cheap, got out some green spray paint and doubled the price. It's dropped off over the last few months, but it was rife over the warmer months.