You're right that such a plane in not easy to find. Of the designs mentioned so far, the Sonerai is a marginal two-seater in terms of gross weight and definitely not for aerobatics two-up, the Velox is a custom-made single-seat aerobatic aircraft and none of the Fisher designs are aerobatic at all as far as I know.
There is an old expression in engineering and software design, "Fast, good, cheap. Pick any two." You should also try to prioritize your wish list in terms of what's most important to you.
There are a number of classic homebuilt two-seat biplanes that would suit your needs but without folding wings. Acro Sport II, Starduster Too, Skybolt, etc.
There are also some less expensive modestly aerobatic designs that would work, but again the folding wing issue is tough to manage. Rans S-10 comes to mind and a number of classic, high-performance low-wing designs like the Sequoia Falco.
For a relatively inexpensive (though not cheap) aerobatic two-seat monoplane there is also the Dan Rihn DR-109.
After that there a quite a few folding-wing homebuilt two-seaters, or with glider-style removable wings like the Europa, but they are not aerobatic.