Not true. It surely was many years ago when it was introduced, but other manufacturers caught up quickly and now you have plenty of alternatives.
Also, don't mistake the RPi Pico with other models; the Pico is a really nice product (probably the most innovative one since the 1st RPi) but plays more in the Arduino field rather than with other Raspberries. It can't run Linux for example.
Here are some prices of boards one can actually buy. All in stock (often hundreds of pieces available for each model), most cheaper than the Raspberry Pi models and all can run Linux.
