Don't know how cheap Cavani will be, but I thought the reason he was available was because he didn't like not playing in his preferred position. He is bound to have the same problem here. Aguero is our 9.
In terms of a forward who fits the bill (I.e. can play wide and move to the Middle in the absence of Aguero) the 3 obvious choices are Dybala, Aubemayang, and Griezmann.
I personally would have gone the really young route. Bring in Ousmane Dembele and Gabriel Jesus, not necessarily as replacements for Aguero but jut great young attacking talents.
I'd show faith in Nacho and Sterling's ability to hold the spot down if Aguero has short term injuries.Most want someone serious who could sub in. My sense is that those players are already here in Sterling and Kelechi.
But I understand those who worry about Aguero's injury history and want someone well established who can also play wide. Those 3 above make the most sense for such people.
If it were up to me, I'd set my eyes on Dembele and Jesus.