Hi again!
I'm guessing you're considering starting from scratch due to the possibility of a bought account getting recovered (which is high).
Let me first say that RS3 has become increasingly easier in the past years, so leveling up today is much easier than it was before. I'm confident that you could have max combat in runescape in 1-2 months easily. However, if you're referring to max cape then that's a whole different story since it involves not so pleasant/fast skills such as farming, runecrafting, slayer, agility... all of which take at least a couple of months to get to 99.
I'm guessing it would take you at least 1 year, maybe more. To put it in perspective, I started playing rs again in December (had been out since 2012) and when I started my account was combat 117 with 1900 total level (~90m total xp) and about 5 99's. In the 5 months since, I'm already 138 with a total of ~2550 (~550m xp) and about 18 99's [2 120's].
In summary, if you have a passion for the game and don't mind starting from scratch (level 3, 0 quests, 0 99's, etc) then It's a good deal. This way you'll always know 100% that the gp you buy is safe and there's no way that you'll lose it in case someone recovers account. However, if you do mind grinding and having to start from scratch, you'll easily get bored and leave the game in no time, thus wasting that 1b.
I guess it's a matter of how patient you are and how willing are you to put your in-game wealth at risk. Either start from scratch but be certain that the account will always be yours, or simply buy an account from a trusted user and hope that it never gets recovered.
