The prices of silk sheets are changing all the time as the price of silk fibers are changing.
Different silk sheets, even if they are all are 100% mulberry silk sheets, have different prices.
The quality of the silk sheets, the production, and many times even the place where the silk sheets were cultivated will affect the price. For instance, Chinese silk is better than Thai silk. Thai silk is better than Indian silk. And, you can immediately feel the difference.
You have to go ahead and pay for the most comfortable silk sheets on the market, if you are considering shopping for 100% mulberry silk sheets. Do not buy a pair of cheap (fake) silk sheets.