Technically it expensive because demand exceed supply. Russia was just one of the larger producer, as it is a by product from natural gas extraction, so with the war that source was cut off.

In combination, US military decided to sell a large portion of their stored helium to a single private firm around the same time, rather then sell it off in smaller chunks, and that seems to also have decreased the global supply.

As a semi-new idea people are experimenting with hydrogen as a replacement for helium, which could become much cheaper and renewable compared to helium. Time will tell how bad idea it is to mix high pressure, oxygen and hydrogen while under water.