German post-war glass doesn't have much of an established market value. It's a bit of a pioneer field for collectors and prices are generally still low, with the exception of a few bigger names (unique signed pieces will fetch of course a higher price). This Ichendorff is a relatively well known and beautiful piece, but it's not rare in my area (as I live in the Netherlands, which neighbours Germany). I've bought mine for EUR 20 last year, but I've seen them go for less and for (a bit) more. But of course, that's in Europe. There is no telling what US buyers might make of it.
Good luck with your auction,