If a speaker has a fixed set of conditions, fixed before even hearing from the parish, that to me is a bad sign: “Sure I’ll come IF you pay me what I want.” Can you imagine an Apostle saying that? Jesus told them:
Mat 10:7 And preach as you go, saying, ‘The kingdom of heaven is at hand.’
Mat 10:8 Heal the sick, raise the dead, cleanse lepers, cast out demons. You received without paying, give without pay.
Mat 10:9 Take no gold, nor silver, nor copper in your belts,
Mat 10:10 no bag for your journey, nor two tunics, nor sandals, nor a staff; for the laborer deserves his food.
Food - yes. Pay - no. Holy things cannot be sold. That is simony.
Also, counting the audience is not a measure of success. The question ought to be, “What are we attracting them to?” An entertaining talk? Excitement? A big name? An ecclesial celebrity? “In the old days” a parish mission was focussed on renewal - to ignite true spiritual supernatural fervor and zeal for the Lord and His Church. I have heard too many speakers in more recent years come with a mixture of stand-up comic, dramatic story-teller, and salesman (“motivational speaker”). Such speakers can be entertaining and engaging - but is there depth there? Is the supernatural present, and not merely a well-rehearsed natural presentation?