There are a mix of YHAs and Independent Hostels all around the Coast Path. Prices vary from £15 per night upwards. Some do breakfasts at very reasonable prices, others are completely self-catering with a basic shop in case you need to buy food. They normally have dormitory rooms as well as twins, doubles and family rooms. It is always worth while becoming a member of the Youth Hostel Association. You get £3 off per night and a variety of other discounts at shops and other services. You can become a YHA member at any age. I enjoyed staying at YHAs. You meet great people for all over the world, many of whom are walking the trail with you.
Independent hostels offer a variable standard of accommodation. I recommend reading the latest online reviews. The Cohort in St Ives was one of my favourite places to stay. Others were less good!