I have collected some 90K miles on Delta although I am yet just a Silver medallion.

Recently I have tried to book tickets in the YBM fare category that will allow you to use miles for upgrades. However, every single flight I look at come out prohibitively expensive and in some cases more expensive than purchasing an outright business class ticket.

I am wondering whether I am better off switching to another airline altogether, or whether there is some trick I don't know about?