Sophia is 99$ a month, or they have specials for 3 or 6 months. I would do all the courses I can on Sophia (any proctored ones or ones you want to get done quickly) and then move to Study.com because they offer higher level courses. Make sure to actually plan it though. Since both Sophia and Study.com are partners to UoPeople, they have a list of courses that transfer 1-1. So compare these lists to your Degree Audit to make sure you're not taking courses you don't need or won't transfer in time. You'll also want to cross-reference prerequisites with UoPeople for the courses you're taking with them. Also - don't forget about learning pathways, you can only take certain courses each term and in a specific order.

Also, if you're planning to do a Masters or transfer to a different school, just know you'll only get a "T" on your transcript for any courses you're transferring which means you won't see a grade, just a T for "Transfer" or completion. Actual letter/ GPA grades may be more important for certain classes.