The question is more like how much to set up a company and requirements to get a Non B. You’d probably need to get an accountant or lawyer to do this. Estimate cost about 60k but that could be wildly off the mark.
If you use an agent to bypass the funds requirement then you’ll be stuck on the agent train until you enter on a clean stamp and start afresh.
If you use an agent just to push paper and bypass queues but fund the visa/extension yourself then there would be no reason that you’d have to use them in future.