I don't think there have been many keepers better than Cech over the last 10 years, certainly not in this league anyway. I personally think he would be a cracking signing but I don't think getting a keeper is a priority, if someone like Cech wasn't available would we even be having a discussion about a new keeper?
Jury is still out on Ospina but I don't think I would categorically say he's not good enough. Chesney is a good keeper, the better of the 2 I think, but he's attitude is questionable to say the least. I think having been booted out the team he'll be better for this experience next season, perhaps the kick up the arse he needed. I remember Lehmann came back as a beast after Wenger dropped him in 2005.