A personal statutory letter costs £34.99. An organisation letter, for bodies issuing their own responses and decisions, costs £84.99. You pay per letter and there is no subscription.
Every letter includes the relevant legislation, a dated timeline built from your own account, a clear deadline for the other side to respond, and the escalation route if they do not.
If you cannot afford a letter, you can apply to the Pay It Forward Fund, which is paid for by donations from other users.