Having a large tank will be much easier to keep compare to small tank. Its a good choice for you to opt for a large tank that your pocket allows.
Before anyone reefer can assist you on your question, maybe you can let us know what will you be keeping? Reef tank with mix hard and soft corals? SPS tank? LPS tank? Basically different setup will need different type of equipments and requirements etc.
Averagely for a 6ft tank with equipments, you be spending @ 9-15k and that depends on the equipment you choose. Obviously if you opt for branded equipments, the price will be more expensive.
cost savings only if you opt to purchase used equipments. If you can find a good used equipments, than you can cut cost in your spending.
Cheers