I've never used Delta Cargo, but FedEx and UPS both have on-line calculators that allow you to determine exactly what it will cost (and I've used both). The price on both of those carriers is sensitive to size more than weight. Rates also depend on the origin and destination zip codes, how much insurance you want, whether you want home pickup and delivery, whether the delivery is to a business or home address, etc. I've spent a lot of time playing around with the calculator to see where the price jumps are. I wanted to use the largest box I could without incurring a steep penalty.
If Delta Cargo doesn't have an on-line way to determine cost (and I don't see one), then I'd steer clear. I also agree with Pete that I don't want to give a bike-unfriendly airline my business.
I assume you're talking about sending your bike on a flight that you will not be on.