Low ovt for baeball posters - something under 800 searches a month, and this IS Baseball Season.... nevertheless, allposters.com does pay like 20% commission, so the site could pay off in a small way, if you focus the site completely on that traffic. Since there is undoubtably more traffic for specific teams and players, I'd have a page for each team in each league, a section for All Stars, again linking to a page for each all star, with a link from a sidebar to related affiliate commission based sites, such as Stub Hub for baseball tickets, art.com for more posters, perhaps even ebay for autographed items - though eBay is a last resort, IMO, their affiliate program just doesn't inspire me. I'd also include in the sidebar a link to a few of the sports jersey affiliate programs.
JMO, but I like product specific domains like this, but they can be a bit of a challenge if the item is too small of a niche. Nice commissions on this product, though. One other thing that might help would be to build a network of related domains, such as footballposters, etc., and link them together.
Good luck with it!