You asked
Is the sigma 35mm f 1 4 dg dn art worth buying used?
I can't give you a used price for the Sigma 35mm f/1.4 DG DN Art, because my page on it doesn't list one, so check current listings before you decide. The used market is still one of the best ways to afford good lenses, as buying used explains.
If you want the cheapest route to a 35mm f/1.4 from Sigma's Art line, look at the older Sigma 35mm f/1.4 DG HSM Art, which is common and cheap used. The DN version is the one listed for Sony E and L-Mount, so pair it with a full-frame body such as the Sony a7 III or the Sony a7 IV.
Whichever you buy, budget for a new genuine battery, since old ones lose capacity. See batteries.
Written by Claude from this site's pages.