I currently am in f2p. My training has brought me from 77 to almost 80. But, I plan to RuneScape gold join in the near future and receive an'skill' cape. Although I don't mind cooking or flitching, I would like an'skill crate. I also do not want to have to learn to cook. I wanted my 99th birthday celebration to be memorable therefore strength was the ideal choice. What is the average time between 80 and 99 str be and where would you train? It depends on where and the amount you're willing to spend for pots/good meals while training there.
First, I want to mention that the strength skillcape is now as well-known as the one for cooking or fletching. You can focus on mining, slayering or runecrafting. If you are willing to work hard and learn, these skills are attainable cheaply and quickly.
Let's get back to your question. Where do you train strength? There are a few locations I'll list: Pest control. Although this is an extremely popular choice, I believe it's a poor option. The new pest control system is not very fast and won't provide you with any hit points. It's also frustrating and boring at times. Training from level 80 to 99 will take between 8 and 10 weeks.
Giant Skeletons in Damisthe lair. This is my favorite place to train. It's only possible if you have guthans. This is where you can learn how to use a salve ammy. It gives you an additional +15% attack, and the ability to kill undead. You will need guthans to travel to the bank. If you don't have it you can find other alternatives. This is slightly quicker than pest control and even more so if you have super pots. It could take 7-8 weeks here.
Bandits. They are the simplest alternative, but they are also the slowest. Bandits will automatically attack you when the items you have in your sara or zammy are easily accessible, like a cape. This means that you can simply locate a place, then leave your computer and buy OSRS gold the bandits won't stop at you.