FC house pricing is appropriate for the size of the FC. Large houses are for FCs with 100+ members. Small houses are for FCs with <20 members. If you run the numbers, each member's contribution doesn't get much higher than 1 million gil each which is actually about the same as leveling 1-50 three or four times (I made 300k from my 1-50 ACN), regardless of house size. If you're a tiny FC with 10 members, 625 million is an outrageous amount of money but that's because those huge houses are NOT DESIGNED FOR A COMPANY OF THAT SIZE.