IMO, if you are looking at flat rate placements, and you know that a banner will generate $4,000 in monthly affiliate revenue for you, then obviously $4,000/mo would be the basement. Obviously this should be even more than that since you would be expecting on-going revenue from the players that signed up, so a better calculation would be what a banner generates in new sign-up revenue over a 3 month period, that might get you closer to the flat rate amount you would want to charge.