You could buy your own external power supply and I could chop $60 off the price of the kit. You'd need 10-11v at ~30w (I supply a PS with 60W capacity) and 16/-16v (17-18 would work too) at around 20W (I supply 40W). If you were to bypass the on board linear regulators then you could supply the exact voltages.
Those capacities assume a fully decked out vintage model. I have not measured the actual current draw of the computer. But the cost of the supplies doesn't change, so I don't try to skimp.
And here is the kit for comparison: