about the FR4 pcb price, if you just climb one stair up the ladder to like low end Roger
Rogers material is not just one step above "FR-4", because "FR-4" doesn't really mean much. It's become quite a generic term.
At its most basic level, FR-4 is a garbage-grade material one step above FR-2/CEM. But no one actually buys that anymore (at least at our level; it is still used in extremely cost optimized designs). Rather the term "FR-4" has come to apply to any material that can be
processed like FR-4: it follows the same manufacturing flow, and is the same sort of stuff (E-glass–reinforced epoxy), so it's acquired the same name. These materials are more properly called "FR-4 compatible", but the nomenclature is what it is.
High-quality lead-free FR-4–compatible materials are very good indeed. Some of them are optimized for signal integrity, one example of such being Isola's FR-408. This class of material is where one should look if one wants the best signal integrity per dollar.
Rogers-class materials do not use traditional FR-4 processing, so their extremely high cost comes both from the high base material cost and from requiring a different fabrication flow. But they are, nonetheless, where you have to go for deep RF designs.