Personally I think you should get a barbell. For the fact that the exercises were designed to use a barbell. Although, I think in the past Cathe or someone has commented that you could use dumbbells. I think that using a barbell instead of dumbbells is a matter of the distribution of the weight to effectively do the exercises. Does that make sense?
I bought a barbell with adjustable weights and I think it was only about $40. If you can't get one immediately go ahead and use dumbbells then buy a barbell when you can.