I had a Walker Bay Genesis Deluxe console RIB. It was a 310. This setup gave you a console with a seat beside it, two seats across the back (one space was for the operator), and a seat/step/locker with a cushion at the bow. I could carry 4 reasonable sized adults with each one having a seat. It was more comfortable with only 2 people on board, but could carry a full load when necessary.
If you can find one, a console by itself will usually cost $600-800 (the St. Croix one is ~$1300). Then you will need to add controls. Usually it will have to be shipped as freight.
Some RIB manufacturers offer consoles for their boats, getting one on its own can be difficult. They are not usually stock items. Also most console are designed for a particular model boat hull, fitting it to a different hull may require some work.
Grand Boats has a nice console. It is for the G340 RIB they sell. The console is not shown individually in their catalog, but should be available if you ask them. Don't know how it would fit in a 310. I was looking to put it in a 470. It is about $800. Grand was the most responsive company I dealt with when trying to get a console. Since it is made in Canada you have to arrange for importing it.
Nautica (in FL) also has some consoles.
Boyd at Annapolis Inflatables used some pretty small consoles laying around (not shown on the website). Maybe he still does.
Todd manufacturing also used to make some consoles for small boats. They were less expensive, but you got what you paid for.