As long as you keep in mid that the $150 is to see if its a fad or not, 2nd hand machines are good.
The gaggia classic has a solid build, and uses many std parts used by other manufacturers.
But if you can pick-up a sunbeam 6910 you can steam and make coffee, or a 6900 will still steam and make coffee. As always condition will play a big part.
Factor in a descale (DIY), and group gasket if it is old.
The biggest downside to entry level machines Ive found are aluminium parts, the gaggia will have the least amount of these on your list (at least I think so, I could be wrong).
If you make 100 coffees, its paid for itself.