2002 Pontiac Sunfire won't take gas

My 2002 Pontiac sunfire suddenly does not take gas. We were almost on empty and tried to put gas in and it spit it back out. My husband used a snake type thing to see if someone had shoved anything in the tank and they had not. We can actually put gas in the tank however we have to put a little in and let it go down and then a little more etc. And it is taking us 20 minutes just to put $10 in which is no good at all. Do you know what this is and if so is it costly to fix?