Now, I have been working towards my quest cape for more than 2.5 years. It's so simple to get. Faster than the majority, and even all 99 skills depending on RuneScape Gold whom I'm being told. I was told this time and time again, and I was very bored, so I decided to do some calculations.
Add all the abilities required to get this level of experience and you'll have 11,492,440. This is just below the level 99 for any skill. Wait, there's also a level 85 fighting requirement. There are only 40 attack, 65 defense and 69 strength are required. Additionally, there's a 55-pray, 75 magic, 75 ranged and 41 summoning. Add it up with the default 10 hp, and it only comes out to level 66.9. To reach 85 combat, you need to increase attack up to 60 and HP up to 61. This brings the total xp to 12,030,092.
However, there's more. It's reasonable to assume that you've got 65 defense, and at the very least 69 strength. If you have 75 ranged and 65 defense and you have 65 attack, 70-75 horsepower, depending on how you train. The probable total is between 12,641,117 to 13,113,911. It's just 89 levels which means you'll have a real difficult time obtaining the quest cape at that level. It is possible to get it at this level, though we'll just leave it there and give ourselves a conservative estimate.
Remember that a 99 is a skill that has 13,034,431 xp. The training to earn the quest cape is to be as hard as any other 99. This is especially true when you consider that most of the training is at the lower levels. Comparing it to training in the 99-level F2P range. It's a lot harder to reach 13M xp when you don't have the access at higher levels, something that member skillers often consider to be a given.
However it's not enough to just learn to make a quest cape. You must actually do the quests! Let's make a rough estimate for a second. The 159 quests take about an hour each, if you have a guide (which they do for me, at least). Even if you're a fervent RuneScape player and play 4 seven days a week, 24 hours a week, it'll still take you five weeks and five days to finish the entire game. Now assume that you'll have to wait for an average of 10 minutes in between each to get prepared for the challenge, which increases it to Buy RS 3 Gold six weeks and 5 days.