RR Price

I've seen in the FAQ that-
0 - 250 referrals price: 0.15 each
250 - 500 referrals price: 0.16 each
500 - 750 referrals price: 0.17 each...

Now, when I bought 300 referrals pack, the price was 45, but it is more than 250, so the last 50 falls in the 0.16 range... then why the price is 45?

Next 300 referrals cost me 48 USD... Need to understand the same thing, as, last 100 falls in the 0.17 range...

And finally, please clarifiy one thing, say I have bought 600 referrals with 45 and 48 in two phase. Now from next month, when I extend, do which rate does apply to me? Do I pay a fix rate for everybody? If so then what is that rate? Do I pay for 0.16 for all 600 of them?

In other words, I have bought 600 referrals at 93 (45 + 48)... Now when I renew all of them, do I pay at 0.16 for all of them?

The price is based upon the rented referrals you already have, the price doesn't include the ones you want to purchase.

Say I have 900 referrals. How much will it take per referral to renew?

When bought, each 300 cost differently (45, 48, 51). Is the renewal price is different too?

The amount of referrals you have determine the price.
If you have 300 rented referrals and want to extend them, the price will be 16 cent - discount for all of them as described here: https://www.adzbazar.com/index.php?view=faq#4