I have run a number of studies with incentive paradigms. There are several ways to do this without spending any/very much money.
One of my favorite methods that works quite well is called a "hall of fame" manipulation. The paradigm is set up such that participants earn arbitrary points during the task. After I explain the rules of the game, I explain that they will have a chance to make our hall of fame, which is simply a high scores list. It's made up, but it comes up on the screen for them to view, and they are asked to enter in a user name in case they have a high enough score to make the list. Of course, for anonymity I don't actually record their user name or update the list based on participants' performance. At my school, undergraduates seem highly motivated by this because they are competitive.
Another thing we do in my lab is associate arbitrary points with earning candy at the end of the experiment. I like this manipulation less because many undergraduates are trying to watch what they eat, and are not very motivated by this. However, in combination with the hall of fame list, it seems to work quite well.
If you are able to get a little bit of money, what you can do is buy one Amazon gift card for say, 50 or 100$ and tell participants they'll win raffle tickets which you will draw from to select one winner after you've run your experiment. This has obvious pros and cons, namely, it's good that you don't have to pay each participant, and it's bad because some participants will decide that they have no chance of winning the raffle and they won't be motivated by it at all.
Finally, another option that is good for if you want to have several levels of incentives is to use symbols during the experiment such as: \$ for low incentive, \$\$ for medium, and \$$$ for high. In reality these amounts can correspond to pennies, allowing a participant to earn, say, $10 max over the study, but they don't have to see on each trial how minuscule the money is. The symbols will motivate them more so than the amount of money would.
Given that you are doing this for a course, I recommend using points and a high scores list.
One thing that is annoying about doing an incentive manipulation is that if you fail to find an effect, it may be that there is no effect of incentive, or it may be that your incentive wasn't strong enough; you'll have no way of knowing. As with any study, a good idea is to have some other aspect of the data that you're interested in studying so even if your incentive manipulation isn't successful, you can still address some other question.
Hope this helps! Good luck.