You can sell your ebooks through Amazon's Kindle program or Apple's iTunes Connect, which gives you access to a large majority of the digital-book reading market and the barriers for entry are incredibly low. You don't need to invest lots of money to make this happen, but you do need to invest lots of time, not only in writing the ebooks, but in marketing them as well.
Getting a raise is an excellent move because it doesn’t require you to trade more time for more money. You are putting in the same amount of time, but pulling a bigger paycheck. But, it’s always a bit tricky to ask for a raise when your company already has you at your current salary. You’ve got to make a strong argument you deserve the increase. Here are the top 10 mistakes to avoid when asking for a raise. https://www.facebook.com/Buzzing-Offer-Digital-Marketing-1107247206148320/
However, like anything else truly worthwhile, apps require a significant investment of your time or money upfront. If you don't have the skills, then you have to hire someone who can assist you in creating a great app. But first you need to come up with an idea that will sell. Do the proper market research and analytics to come up with the right app.