If difficulty is very high, then acquiring a bitcoin by mining is expensive.
that is correct, with rise in difficulty everybody will get less bitcoins, as new operators who entering mining will take their share. With running cost same and let say price of btc same, miner who got less btc will not be interested to sale at this rate and will wait till rate increase. To upgrade hardware miners no need to sale btc, but asic manufacturers will sale, but those are cleaver guys and they understand well, miners will buy asics when btc is higher.
it is interconnected process and it cant be otherwise. if bitcoins price on lower side miners will not sale and that will reduce amount of btc in circulation, resulting in price rise.
According to some previous analysis of blockchain 70% of mined coins never enter into circulation. If price of btc on lower side that can be 90% or higher. for example I sale 3% of mined coins, if btc price will get up to 120 I will sale more.
Difficulty rise and rate of btc both influencing mining in many ways. So to say that diff and btc price not correlated not correct.