What is the best cheap mac for a homeshool highschooler?

I'm 13 years old and will be a freshman next year. It's always been my dream to have a mac, but they're just so expensive! I'm currently saving up to buy one, and my parent's will pitch in, but I need to pay for the majority myself.
I do photography on the side, so I will have a lot of photos on my computer. I'm thinking of doing online school next year, so I will be using it often and since I homeschool, my work comes with me wherever I happen to be going that day, so it needs to be lightweight. Having a DVD slot would be nice, and I will probably have to buy a refurbished one for under $300.
Please give suggestions on what model you think would be best for me.
Thanks!

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