My maths prof wrote his own textbook, we had to buy it but it cost I think £40 new and covered everything we needed for a 3 year physics degree and you could easily find a used copy near campus. Still got my copy somewhere.
I think it was the only textbook I actually needed, all my lecturers wrote their own courses and extra reading tended to be from journals. Only other book I remember using regularly was the CRC Handbook and those were just scattered here and there around the department.
I sometimes suspect that the push for decimalisation was in part to avoid having to teach computers the old system.