No respectable hair transplant surgeon will perform the procedure without the patient having a clear understanding that a 5-AR is a must. The results without one are horrific, because further loss won't be in the regular "male pattern" but in sick looking patches.
A really good one will tell you to be on a 5-AR for a year first to stabilize your hairline and make your donor follicles as healthy as possible.
The whole "fuck 5-ar's I'll just get a transplant when the time comes" is a brutal misunderstanding of the reality.
The industry does a good job of hiding this fact though. By the time a transplant is considered, most guys are finally willing to use a 5-ar at that point because they're desperate. But the irony is earlier use would be prevented the need for a transplant to begin with.
If nothing else you need to establish whether you can find a tolerable, side effect free dose of 5ARs before committing to a transplant. Some can't seem to so may as well save your cash for a toupee, hat collection, or razor and wax.