Only other engine I can think of is the Z18XE from the Barina XC SRi or TS/early AH Astra. Another member on here (@Chris R, who has nothing to do with me) has done this swap on his XC Combo.
Z18s in Astra form are usually dirt cheap, but the swap does take some effort. And unfortunately, Z16SE engines only appeared in local Combos and no other locally sold Opel, so yeah I can see why they'd be so expensive, given they probably share a lot of internal components with the TR Astra's C16SE. Legally, you can't fit that engine either, due to it being older than the car you're putting it in.