There are so many great options for this! Depending on your budget and your DIY skill level, you could build shelves from scrapwood. You could also build floating shelves. You could even ziptie together crates for shelving. Here are some of the tutorials we have on DIY shelving:
Simple Shelves & Cubbies - https://www.justmeasuringup.com/craft-room-makeover/
Scrap wood picture shelves - https://www.justmeasuringup.com/picture-ledges/
Sliding storage shelves - https://www.justmeasuringup.com/sliding-garage-shelves/
The cheapest way is to build them your self. Floating shelves are super high end looking.
How cheap? Head over to any big box improvement store (or hardware, or Walmart, Target, etc.), and take at look at the options. There is everything from inexpensive metal brackets and vinyl coated wire shelves to a bit more upscale decorative wrought iron or wood brackets and many pre cut wood shelves to choose from. Just depends on your budget and application!
The cheapest way to get shelves is to build them!