Superheating runite ore is a great free to play Runescape money maker netting around 1.5-2 million gold per hour. This money-making method is very simple. All you need to do is repeatedly cast the superheat spell on the runite ore in your inventory. This method will also net you pretty good smithing and magic experience in the process of making your money. A more detailed guide can be found in the video linked below.
Some great websites to look into for promoting your side business are Fiverr.com, Upwork, and Odesk.com. Remember that when you set up profiles for these websites, you are representing your company and your brand. Describe your services in great detail. Make sure that you have no grammatical errors in the description. It’s also wise to include a portfolio, links to your work, or recommendations from others. Additionally, remember that if you choose to build up a side gig business, reputation is everything. Whether you are working for a close friend or a stranger online, make sure that you always produce top quality work so that it can lead to referrals down the line.
Level 30-60: Cut Willow logs. Willow logs are fast exp, but their locations aren't normally quiet. You won't make much money with these trees, but enough to buy a Rune Hatchet (requires 41 Woodcutting). You can get magic seeds worth up to 150,000gp from birds nests here. Skip cutting down maples. These become available at level 45, but they are slow to cut down and not as good money per hour as willows.
Another way to make money if you only have a few days is to sell items on eBay. You can typically set items to sell in just a few days, and you can have the money in your PayPal account instantly. If you are going to sell on eBay, you have to have excellent pictures. To achieve this, make sure to take photos of your items in a place where they have enough light. Make sure pictures aren’t blurry, and write as much detail as possible in the item description in clear, easy to understand English.