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I can only think of five eyepieces that meet your criteria.
AP SPL, I mention this one first because they are out of production and you will never find a used one at 4mm, so they can be ignored.
TMB SMC, again hard to find, but I managed to assemble a few. Only 30 degree AFOV though, and they only perform well in long focal ratio scopes.
Takahashi Abbe Ortho, available new and the obvious value choice.
ZAO I and II, the best 4mm planetary eyepieces ever made. You don't indicate a price guide, but I might consider selling my 4mm ZAO II for $1100, as I don't have much use for it.
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