It is worth your time to at least check online to see which one is cheaper. The other store will usually not only match the competitors price but will further discount your purchase.
Both Home Depot and Lowes are great stores to shop at for home decorating and improvement. There isn't a clear answer to your question, as it depends on your location and the actual item you are seeking. You can easily use Google to search the items you're looking for at both Home Depot and Lowes, and then decide from there.
Cheaper isn't always better. You have to consider the padding and installation. The type carpet matters too. You don't want to spend your time and money cleaning cheap carpet.
Take some nice flowered bedsheet of single bed. Decorate it with some artificial lowers or some decorative item which can be easily used. It will give your house a new look.