Question about selling platinum ring with 28 diamonds..value and where to sell?

I have a diamond plattnum ring that has about 28 diamonds in it..I am certain it is worth a lot but not quite sure exactly how much...how can I find out it's worth..I would like to sell it but I'm not sure if a pawn shop/jewelry/coin store will give me it's worth...What should I do, how can I find out its value..and where would be the best place to sell it? I am soo behind in my bills I need money ASAP or my water, and electricity will be shut off..plus my registration on my car is 2 months behind and the list goes on..I really need to take care of all these things but I am not sure where to sell this ring I really need to make payment for all these things by Wednesday..I'm not sure where to sell this and get it's true worth? How and where can i get it appraised?