The same account can differ in price several times over depending on what ships with it. Here is what each item buys you in practice.
Session files
The mandatory minimum. Without them there is no account — there is a phone number you have no access to. On formats, see account formats.
Cloud password (2FA)
Needed almost always. Without it you cannot change the password, close other sessions or recover access. An account «without 2FA» usually means a password is set and you are not getting it — somebody else's control over your asset.
What to do with the password on day one: changing it. Why two-step matters at all: here.
Useful, not critical: Telegram uses email to reset the cloud password. If you hold the password and have changed it, email is a fallback rather than the main route.
Access to the number
The priciest and the most temporary. Access is usually rented for a term and disappears with the number — risks are in virtual numbers. Worth paying for only if you plan to recover access by code.
What to buy
Session plus cloud password is the working minimum and covers most situations. Email is a nice extra. The number: case by case, knowing it is temporary.
How this shifts the lifespan maths: how long an account lives.
Buy accountsaged, with full session files