This is a source-dependent trivia figure drawn from an introductory mainframe tutorial arguing that mainframes are no longer prohibitively expensive. That source cites roughly \$50,000 (late 2006) to buy and configure a complete entry-level IBM mainframe with software, storage and support under standard commercial terms. Of the offered options (\$1,500 / $50,000 / $35,000 / $75,000), $50,000 matches the intended source answer; \$1,500 is far too low for any complete system, and the others are near-distractors. The exact number cannot be independently verified against IBM price lists (entry z9 BC list configurations were often quoted near six figures), so this rests on the specific courseware the question was authored from, where \$50,000 is the stated figure.