New "street" price on a stock Sonus 5 (no upgraded preamp or fancy top) should be about 2300, 2600 for one with a fancy top and upgraded preamp. If you find the right dealer at the right time, you might get the fancy one for 2200-2300, but that's very unusual.
On resale, they move slower than, say, a Sadowsky, mainly 'cause the Sadowskys are what people are hot for right now, but it should pull anywhere from 1400-1800 in mint condition, depending on the model. The bass in question probably cost about 2200 new, also adjusting for price increases, assuming it's a few years old, so if it's mint, 1100 is probably at least 200-300 less than it's worth... which, IMHO, is a great price.
As you may or may not know, high end basses don't follow the simple rule of "1/2 what you PAID* new" for used (*=selling price, not MSRP). Depends mostly on how badly the seller has to move stuff (as usual). If yer willing to wait for the right buyer, it makes a big diff.