I can vouch for the principle of used lab equipment, most professional grade equipment have multi-decade lifetimes. Further, refurbished with warranty is the best way to go. We are located in Europe, and have had excellent experiences with LabExchange, they offer 1 year warranty with the option of adding a service contract. We have no experience of the US market, however.
I agree with the previous answers, re-furbished equipment is a great way to stretch your money. As long as the incubator has new filters, you should be fine.