"Purchasable with a large amount of credits" is a given, as close to gospel as we get around these parts until and unless someone declares it apocryphal.
But what if they were also hirable for a more reasonable but still significant weekly or monthly rate, either as a pure rental or as purchase installments? It would open carriers up to pretty much anyone, solo or squadron, who could use them to earn enough credits to cover the rental and still make a profit. If the rates scaled with carrier size and/or number of active docking bays this would also provide some parity between squadron sizes; more CMDRs would make more money per unit time, but the carrier rental would be higher.
Fail to make your payments, the carrier is repossessed and you can't hire another until you have at least one payment in the bank. Super-rich CMDRs could still buy them outright.
There would need to be some workaround for deep space explorers, maybe some sort of IOU based on systems scanned but not yet handed in.
But hey, this is just spitballing. It's ED, so we'll likely get an initial cost that's either ridiculously low or insanely high, followed by one or two excessive reactionary nerfs or buffs, after which everyone will just come to accept wherever it ends up by default.