I had a cheap set I got at Walmart a few years ago for physical therapy. (https://www.walmart.com/ip/Gold-s-Gym-6-Stretch-Bands-3-pk-resistance-bands/54193769, $4.55) Then, after I had used them for a couple weeks, I wanted prettier colors and more types of bands, so I got these from Amazon: (https://www.amazon.com/dp/B087G44DY2?ref=ppx_yo2ov_dt_b_product_details&th=1, $79.99) (https://www.amazon.com/dp/B0971KT4X2?psc=1&ref=ppx_yo2ov_dt_b_product_details, $24.99) (https://www.amazon.com/dp/B093SWH7C1?psc=1&ref=ppx_yo2ov_dt_b_product_details, $7.98) (https://www.amazon.com/dp/B07XGL6S41?psc=1&ref=ppx_yo2ov_dt_b_product_details, $6.99) There are many more to choose from, some cheaper, on Amazon if you're not being picky about the color like I was, or if you like primary colors, black, gray, camo green, or orange.
I also got this digital book, which is pretty good. (https://www.amazon.com/gp/product/B07QJFGG5N/ref=ppx_yo_dt_b_d_asin_title_o03?ie=UTF8&psc=1, $20.99) The bands are so convenient to use in my home office while I watch TV, listen to music, and even read things on the computer. I love them! I'm a skinny-fat old lady, so I really need to develop my muscles, especially legs and glutes, as I approach an all-time low adult weight for me.