My background - been drinking buddies with two different agents and also friends with a national federation physio so I build up some good gossip over the years (and have leaked some news a couple times over the years on here).
There is massive variability with contracts.
Some of the biggest variables dont even have anything to do with either talent or instagram following: two big things are nationality and timing.
Country:
Athlete A is an American in a less popular discipline. Never won a US title but made a few teams. Almost never does Diamond Leagues, and in peak shape is maybe 8-10th in the world.
Athlete B is not American in one of the most popular disciplines. Consistent top 5 finisher at global champs, consistent Diamond League competitor, top 20 all time in their discipline.
The same sponsor offered Athlete A $200,000. Athlete B got offered $70,000.
Another example that pulls in timing as well as nationality would be Athlete C, a recent NCAA champion who while still collegiate almost made team USA for a global games. They went pro, signing the week after US champs for $250,000.
Athlete D had run the marginally faster at a younger age than Athlete C and had already made multiple global champs, but were not American. They didn't have an agent until after making these national teams, and were looking for a contract several months removed from their best performances. They got shoe only offers from two sponsors and $10,000/year from another.
Years later, Athlete C is yet to PR post college, Athlete D is consistently among the top 10 fastest athletes in their discipline in any given year (they're on a better deal now thank God). Athlete B and D also aren't East African FYI.
Even within the USA, timing is a huge factor. Another athlete I know once got offered a contract extension at $300,000/year following Doha 2019 to kick in before their contract expired Dec 2020. They turned it down figuring they could get more money as a "free agent" in 2021 if they had a good Olympic performance in 2020. Of course, covid hits in March, Tokyo is postponed, and the same company that offered $300,000 in October 2019 offered $125,000 January of 2021.