You don't get your mom cheap stuff. You get your mom "inexpensive" stuff. Or else she'll hate you.
Make something beautiful for her. For example... Some cute flower pot arrangement with her favorite flower in a pot and design the pot with paint, add some nice stones to the surface and add some glitter and colorful ribbons.
When I didnt have much money at uni, I would do things for my mum like run her a bubble bath with nice bath bombs etc from lush and get her a glass of wine. Other times I would bake for her, or suprise her with dinner etc.
I make my mom things that don't cost a lot of money and are heartfelt. You can get her flowers or take her out to dinner at a place that isn't expensive.
Nothing at all wrong with picking some nice flowers and your home-made card.......like Cupid's arrow, goes straight to the Heart....a lasting memory.
Make her a home made card, or cook/bake her something. Guve her a hug and tell her you love you. Buy her some flowers.
Get your mom a watermelon and write "I love you mom" on it with oil pastel xD
Or Crayon o-o that should work fine