I passed the 25,000 MQM threshold on Delta this year by spending only $400 cash. A $70 one-way MHT-GSO; a $180 GSO-LAS r/t and a $150 GSO-MHT r/t. Of course, I had a bump-a-palooza during this time, which were redeemed on 3 GSO-LAS, a GSO-LAX and a GSO-SFO round-trip. But hey, that was $1500 extra in my pocket!
I'll make Platinum Medallion this year after spending around $3000 (before vouchers) - inclusive of vouchers, it came out to be around $6000.