I need a rear end for my 1994 Chevy Silverado?

[Hello Darling]

I have a 1994 Chevy Silverado that needs a 3.73 ratio rear axle, but i cant find one anywhere. And what should I pay for one because i have no clue. Iv seen from $500 to $750, but Like I said idk because iv never had to replace on before.