The problem with using wheat is that you need to add plenty of nitrogen to it in order for it to thrive. Not adding N to wheat is about like trying to grow corn without adding any. So the wheat may only be $8-$9 a bag but the two bags of 34-0-0 that your going to have to add per acre is around $14 each....for a total of close to to $40 per acre. Its likely that its going to be yellow by Christmas too and you'll be adding more N or either just accepting that its yellowy for the rest of the year. Cereal rye does not require all of that N to grow....In fact its used by farmers as a cover crop after their cash crops for the very purpose of soaking up any leftover N and returning it their next crops. You can add N to cereal rye to speed up growth in order to keep up with browsing pressure but its not required to keep up from going yellow the way wheat does due to N deficiency. I'd suggest top sewing cereal rye before a rain.