available − fee for 'budget', when a balance was given. null otherwise.
The cash-limited maximum: a quantity for 'exact-quantity', a spend for 'budget'. null
when cash doesn't bind (p_min ≥ 1).
The smaller of the two limits, or null when neither binds.
The largest mint a market takes right now, and what binds it. A snapshot: see maxMintNow.