Looking at it from a logger's point of view, hardwoods in Wisconsin are measured by the
Doyle scale. Diameter is measured at the small end, inside the bark. Assuming that's how you measured the logs, the poplar log would scale out to 175 board feet. If the log were worth $.35/board ft delivered to the mill, that would be $61.25. Problem is, no production commercial mill will take a log under 8' 3", so the only way to sell a 7' log is to someone like you, or for firewood. Depending on the distance, I'd consider $40 a fair price delivered, $25 if you pick it up. That should get you ballpark.
The 8' by 16" diameter (again, Doyle scale) cherry logs are 72 board ft each, for a total of 576 board feet (that would be considered serious cherry in my area). Check locally for prices, but I'd pay $.60/ bd ft delivered, which would come out to $345. If I have a customer lined up for the lumber (which is usually the case for cherry), I'll offer a little more, just to make sure I get the logs. As a cautionary note, look at the ends of the cherry logs for ring shake (separation of the wood around the growth rings) and dead branches that could introduce rot into the log. If there is ring shake, the log can fall apart when you mill it, leaving you with some high-dollar firewood.
That comes to a total of $385, delivered. I'm willing to pay a little more than market value, so that people will think of me first when they've got some good logs that I can use on my
portable sawmill. Again, prices vary. I'm in Missouri, so it is going to be different here, and my situation is a little different from the commercial mills, since I have a customer base that buys odd sizes and shapes.
One last thing... if they came out of someone's yard, I'd pay half as much. No commercial mill will want them, and you'll likely destroy several blades on metal.