Lol, I did answer your question. The cost difference is obvious. Less storage will have a cost and more storage will cost more. I can't give exact figures. If your 90 minute RAW footage at 60fps exceeds the small storage then you'll have to afford more space.
Okay, I'll help.
You're spewing out thoughts that you cannot back up. You may be halfway right, but for the wrong reasons, and you have no idea how to get to where you think you're going here. Honestly, a few minutes with Google will tell you what you need to know.
If you're shooting on film, frames=feet=$. 60fps vs. 24fps. effectively more than doubles the cost (250% to be exact). With film, you pay per foot to shoot (purchasing film stock), you pay per foot to have it processed, and per foot to have it telecined. It's not likely these days that you'll pay per foot to have the final print since distribution is almost completely digital now. If you want a real example of the difference in cost of stock, a 100' reel of Kodak VISION3 200T 16mm film runs about $55. A 400' reel is about $220. There's no drop in per-foot price for buying more. Oh, and a 400' reel is about 11 minutes of shooting at 24fps. $220 for 11 minutes. Just to shoot 16mm (this doesn't even include processing and telecine). Up it to 60fps and that reel only goes about 4 minutes.
That's kind of a bad argument, though, because I don't know anyone shooting film at 60fps.
Now, in the digital world we're just talking about data storage. Camera cards are what they are, and unlike film can be cleared and reused. So, the first thing to look at is how much it costs to increase your storage space in post. A 4TB Thunderbolt drive from G-Tech is $300. So, let's assume (though it's not always the case) that 60fps requires 250% of the storage space that 24fps does. We'd need 10TB, and a 10TB Thunderbolt drive from G-Tech is $550. That's only a 50% cost increase in storage. In terms of production budget, that extra $150 is negligible. In other words, it's dirt cheap.
In RAW, yes, 60fps will eat up more data than 24p, though there are several flavors of RAW and 60p can be recorded without more-than-doubling storage needs. With other cameras/codecs (like Canon DSLR), 60fps is often relegated to a long-GOP codec while 30p and 24p are available in higher resolution, all I-frame codecs. So an EOS 80D actually requires more storage and a faster write speed to handle 1080p24 .MOV than it does to shoot 1080p60 .MP4.
But the moral of the story is that upping data storage by 250% doesn't cost so much that it's in any way cost prohibitive.