Neil,
The co-op I was in is the
Northland Artists' Exposure Gallery in Parkville, MO. The co-op rents the space. Prospective members have to be juried in. There are quarterly dues, a small commission on every sale (20% which is pretty low), and you have to work two shifts / month. Each shift is 4 hours and we have two people working each shift. I generally did both of my shifts on the same day, and since I'm paid to be downtown in an office all week that meant one Saturday a month was tied up. It's a good gallery and nice folks but I just needed the time. Once I get really going with my engraving I might see if I can get juried in for that - 3D stuff
always sells better than 2D. You need both though - they come in to look at the walls but they most often buy from the cases.
The arrangement at that gallery, btw, is that the 2D people get a 'panel' - a 4x wide wall section and the jewellery people get one large and one small case. The other 3D people get a suitable display stand. Once a quarter everyone moves to a new spot so no one gets stuck in a 'bad' spot (there really aren't any in that space) and no one gets to 'live' in the 'good' spot. You swap with another artist and just arrange to be there at the same time to do the switch. We have a theme each quarter to help encourage people to bring in something new.
Check around your area - there's probably at least one co-op somewhere nearby. Even if you
never sell anything the exposure is good, as well as being able to tell people "You can see my work at..."