Rose absolute is cheaper because of the way its produced. I may be wrong, but I believe the solvent extraction methods involved in producing absolutes give a greater amount of oil for the number of plants. The plants are treated with solvent which leaches out the oils and produces a sticky mass. This is then washed repeatedly with alcohol to produce the oil. The downside to this method of production is that some of the solvent remains and that can be a potential skin irritant. With Jasmine it is hard to buy anything but absolute because its so incredibly expensive to produce. With Rose, I personally would always go for Rose Otto rather than the absolute. The aroma is also quite different between RO and RA. I do believe that with Rose, as with most oils, you get what you pay for.
Hope this helps!