It’s possible to store data in the Grin blockchain. About a year ago I put the Mimblewimble whitepaper in the MWC floonet blockchain by storing it as the lock height of several thousand height locked kernels.
At the current Grin block height, 21 bits of arbitrary data can be stored per kernel using the same method. And at the current base fee, the cheapest that a kernel can be added to the Grin blockchain costs ツ0.0125.
So storing 1 bit of data permanently in the Grin blockchain cost ツ0.000595238, and it’d cost approximately ツ62 to store that whitepaper on the Grin blockchain.