I see those prices in the Great People panel and think, "I gather I'm NOT supposed to buy them." As there is literally no way that a player would EVER be able to afford such a price tag. Not unless he deliberately went without spending the more reasonable increments of gold or faith to buy useful things. Saving up such a HUGE amount just to purchase ONE thing is like shooting yourself in the foot. You actually injure your position by NOT spending smaller amounts. About the ONLY thing you get by saving up for a BIG purchase is to have bragging rights to say, "I once spent _50,000_, just to rush a Great Person acquisition!" (And then probably lost the game to some other AI civ.)
It's certainly doable.
I mainly play King/Emperor because I like the more casual pace (as opposed to the stressful pace of playing higher difficulties).
In my current Marathon King game, I bought plenty of Great People for 50,000+ gold. I even bought several for 150,000+ gold. Right now I am netting 3000 gold per turn and I have 20+ cities all doing Commercial Hub projects. (Just grinding it out the turns to get a Diplomatic Victory). My current treasury is 314,000 gold.
I also have 100,00 faith and am getting 1000 faith a turn. So 2000+ cost Apostles is not an issue.
In fact, regarding your prior complaint about the cost of Apostles, when you first get Rock Bands, your very first Rock Band (on Marathon speed) is 1800 Faith and your first Naturalist is 4800 Faith. Thus a 2000 Faith Apostle is actually very much in line with that....
Meanwhile, gold purchase prices:
Machine Gun, Aircraft Carrier, Destroyer: 6480 gold
Helicopter: 7200 gold
Mechanized Infantry: 7800 gold
Nuclear Submarine, Rocket Artillery: 8160 gold
Giant Death Robot: 18,000 gold
Purchase price of districts (variable. this is for my current game):
Aqueduct: 4320 gold
Most other districts: 6480 gold
Canal or Dam: 9720 gold
Spaceport: 21,600 gold
I share these numbers so that those who do not regularly play Marathon can see what the baseline cost is for purchases. As a result, I think the Apostle faith costs you listed are very reasonable....