Or you could go into your career_0.cfg and alter renown to whatever you like,since its hardly realistic to ask you to pay for your own boat is it,personaly I don't think that an arcade element such as renown has any part belonging in a sim.My personal opinion of course

dump the renown to the bottom of your chosen sea and get what you need to fight the enemy

lord knows its hard enough as it is without having to save for an upgrade