I quite like Onana and think he'd be a good upgrade on De Gea. My first choice would probably be Diogo Costa but if Porto won't budge on price then I'd be happy for us to pursue Onana if he's gonna be significantly cheaper
I think each choice has to be even more budget friendly than previous years. The Gaffer will not have the room to blow the budget that he was able to push last year (that's what it felt like last summer).
I'd buy him in a heartbeat. Ten Hag knows him really well, he'd improve our buildup instantly and his shot stopping is equal to De Gea's. Not sure he's got the worldies in him like DDG but overall it's an upgrade.