Try apps like LetGo and Offer Up as well.

When i was shopping you could find something like a mint Cannondale Quick CX5 for $300.

That said, Giant's own website has Affirm Financing available, and they will ship the bike to your local LBS (or if the LBS has it in stock they'll sell it to you).

In case the bike you really want is a tad over your budget at the moment and you'd like the flexibility to pay it off in 3/6/12 months, while also getting the LBS treatment ans post sales support (free tuneups over X amount of time, etc...) Just another option going new if you chose Giant.