The biggest downside of any drug is always much worse than the likely result. I don’t like the side-effect profile of steroids, and tissue thinning is a bigger deal than you might expect. If it were my body I’d price mesalamine enemas (probably cheaper than Canasa) before settling on Anucort.
As far as deductibles go, if you are sure to meet your deductible by the end of the year then there’s no financial benefit to delaying it, or agonizing over it, since it will be spent. In my case my deductible is exactly the same as my annual out-of-pocket max, so I just try to ignore how the expense is incurred - it makes no difference.