The only top strikers who were plausibly within our reach this summer were Cavani and Benzema. But Zlatan has since gotten injured, and Benzema has signed a new deal with Real. There's really no one else in top 5-10 strikers in the world who we could get.
We're best looking at the next rung - upcoming strikers - but those who have 2-3 years of first team experience already. In that category, Aubameyang and Lacazette are the stand out candidates, and I've advocated signing one of them for a while now. Both should be available (Dortmund are struggling, and Lacazette is due a big move anyway), and are the sort who'll develop into very good strikers (if not world class). There are players with similar profiles in lower leagues - like Finnbogason in Holland and Kramaric in Croatia - but I don't count them as having enough top flight experience.
The likes of Berahino, Origi, Alcacer, Icardi on the other hand are a bit too undeveloped for me right now to take a punt and place our hopes on. They've just had about a year of first team football.
There's then a third category - the likes of Doumbia, Jackson Martinez and Luiz Adriano - they've been around for a while and are proven goalscorers. But they're all 27+, and haven't yet made a move to a big club. Not sure what the reasons are, but I don't think it's very wise to waste money trying to find out.