media cost != DR solution cost
You might be able to get 1.5TB tapes for $30, where enterprise 1.5TB Disks cost $150. How much is the fiber connected tape head array you're sticking those tapes in, for an 8 head system with 80-120 tape slots? $60-100,000? How much does it cost to have 32 bays of SATA ports online on a 10G connected storage chassis behind your tape server? About $10K.
Tape may still be the right path for archive, for the small set of data you have to keep more than 3 years after it's backed up, but for short term, near term, and especially the current backup data set, you can re-use that DR HDD 10,000 times, and you can reliably re-use that DR Tape 4 times.
Move your daily backups to D2D chassis, even better still replicated at the block level off site (often cheaper than paying for 4 years of Iron Mountain tape pickup services). Lat that data migrate slowly (using 24 hour windows instead of 6-8) to a low capacity tape system used only for archive, and snap only weekly or monthly archives as required by your regulations because your online D2D chassis already has every version of every file created over a 30-90 day window. Even short term offsite rotations (your daily and weekly sets moving offsite), are cheaper to do on disk than tape due simply to tape replacement costs over time, so even if you can't afford wired data duplication to your failover site or DR storage provider, its STILL cheaper to use D2D for backup than Tape, EXCLUDING long term archive requirements.
As for the benefits of Disk over tape when it actually comes time to recover? How many man hours of IT time are spent every year in your organization recovering files and data that are not in the available onsite tapes from yesterday still cataloged inside the jukebox, meaning they need to be recalled from offsite, re-imported, and wait for an available tape bay then spool the tape to find a file or folder? With Disk, you can restore any file or folder from often several months ago INSTANTLY. How many times is that tape corrupt (per industry averages, 1 in 10 tapes checked has bad sectors or can't be read at all after it has been removed from the site and returned later, if and when the right tape can even be recalled based on accurate data of when a file was even backed up). I've seen cases where it took more than a week to get a vaslid tape from an offsite depot with a valid copy of the server folder needing to be recovered. How many man hours does it even take to rotate all those tapes every day, prepare them for shipping, and more? All that time and potential data loss adds up in real dollars. If you;re not counting manpower, overhead, etc in your costs, you have again failed to properly compare the costs of disk and tape.
I worked for a major DR firm, one that pioneered most of what we use in place today, though you have probably never even heard their name. They did not sell disk or tape, they sold DR software and the server units to make DR happen. In 1998 they had already figured out D2D was better. I did over 400 DR plan designs based around their technology, mostly in competition with Symantec, Veritas, and similar tape products. In every single case we were able to deliver a D2D appliance system at lower cost, hardware, disk, licensing, and rotational media, using their older tape drive as the archive footprint (which works in most cases as what you are required to archive vs back up is usually 25-50% of your total backup size), a complete replacement for their systems, for less TCO. In many cases (almost half) we were able to deliver that system for less than their annual license upgrade price plus a new tape drive, not even considering total competitive system pricing. In every sinlge case, we reduced their backup window by more than half, eliminates issues with multiple concurrent backup conflicts, simplified which systems could back up when, and permitted instant restore of any file for any system. IN about 30% of cases, they also added offsite data replication, which ended up costing less than their pre-existing tape rotation contracts (daily pickups became montly, remaining dollars covered the cost over 4 years of the offsite system installation or hosted partition from a provider).
Disk IS cheaper (for most environments) when you have someone who knows the technology design the data plan. It's faster, its more reliable (offsite rotations can even be RAID sets for added reliability, but disk is in fact more reliable and more durable than tapes to start with), and its easier to meet data compliance and archive requirements with it. It reduces manpower, and it DRAMATICALLY reduces RTO and RPO.