OP’s questions seem to be about least cost for a TA.
Monitor TA’s that do not have a theme , non summer .
In the US Cunard has 1 Sale after another . Some better than others
watch for the ones with Paid Grats , upgrades , speciality dinners ,and OBC, then book.
Find a good travel agent that has a Group for better rate and some amenities. additional .
Cunard permits travel agents to discount their best rates . ( can’t advertise them , must contact).
Cunard does require that you cancel and rebook to take advantage of a lower fare .