The Tsarist Government was making moves, and the Berlin Government was not sitting idle either. Unlike the Russians, with their solid foundations and ample collateral, the Prusso Federation was much poorer.
Use resources as collateral?
Sorry, the Prusso Federation's mineral resources are very limited; the most valuable probably being the agricultural products from the Polish region.
Regrettably, the agricultural crisis had not completely passed, and the international market for agricultural products was still oversupplied, making them barely worth anything.
If it were just a matter of price, it would not be impossible to negotiate. Capital chases profit, and a discount could be considered.
But the key issue was the lack of security. Should the Prusso Federation be defeated, everything would go down the drain, for the Russians would not recognize these loans.
If resource collateral was out of the question, then what about territory, taxes, railways, or ports?