I am pretty sure he said existing RB25 with bolt-ons OR an RB26 which will require the engine to come out. 'Cheap' and 'RB26' are two words that rarely go together in a sentence.
IF the engine is coming out then why frig around with an RB26 (or neo RB25) which does nothing to address the lardy nature of the Stagea. More torque down low as Duncan can attest is a winner.
Personally, I would go the bolt on option with the existing engine as it is the cheapest way to go.
ps. the RB30 can still use low mount turbos.