I bought my Maggie second hand from someone. Just make sure everything is included. There are A LOT of one off brackets/bolts that could slow down your build. The instruction manual indicates everything you need to put it on. I had to order $200 in parts from Magnuson when I bought mine. The seller ended up paying for it, thanks to PayPal.
Just know that you will need all new hoses if you buy a used unit. Possibly a new pump as well for insurance. Make sure the heat exchanger is in good shape before purchase. I got lucky and only had to fix a couple fins. I paid 3k for everything, which included a Diablosport Trinity.