I have 3 places near me and the cheapest is $20 a sheet for 1/8" BB. The grade is B/BB. While talking prices many folks are unaware that all Baltic Birch plywood is not the same. While I do not know for a fact I suspect some of the cheaper Baltic Birch being talked about is a lower grade. There is noting wrong with using lower grades Here is an explaination of the grading:
GRADING STANDARDS Baltic Birch Plywood is graded with a face and back grade designation: B/BB: Single piece face and back veneer. Face veneers are considered clear and free of defects with a light-uniform color. Back allows 3-6 color matched patches, which are oval in shape and egg sized. Inner cores are solid birch single piece veneers. BB/BB: Single piece face and back. Both face and back veneers allow 3-6 small color-matched patches on average and some light mineral streaks. Tight pin knots may be present. Inner cores are solid single piece veneers. BB/CP: Single piece face and back. The “CP†back veneers are downgraded from “BB†grade veneers, which allow for unlimited patches and sound knots, but does not allow for open defects. Inner cores are solid birch single piece veneers. CP/CP: Single piece face and back. Face and back grade veneers allow unlimited sound knots and repaired splits and unlimited patches. The panel is sound both sides and designed for laminating. C/C: Patches, open knots, and small veneer splits allowed. Veneer lap and small core voids permitted. This panel is not sanded and would be used for structural purposes. SHOP GRADES: Shop panels are offered in the full 60†X 60†format in all of the grades listed above. Panels allow for 1-3 splits on the face veneer along one edge of the panel in lengths no longer than 10†and no wider than ¼â€.