MERRICK, N.Y. — Deirdre Yapalater's recent colonoscopy at a surgical center near her home here on Long Island went smoothly: she was whisked from pre-op to an operating room where a gastroenterologist, assisted by an anesthesiologist and a nurse, performed the routine cancer screening procedure in less than an hour. The test, which found nothing worrisome, racked up what is likely her most expensive medical bill of the year: $6,385. That is fairly typical: in Keene, N.H., Matt Meyer's colonoscopy was billed at $7,563.56. Maggie Christ of Chappaqua, N.Y., received $9,142.84 in bills for the procedure. In Durham, N.C., the charges for Curtiss Devereux came to $19,438, which included a polyp removal.