Custom made drawer are not as hard as you think. I mostly but sheets of 2sided finished ply and make my own but in the case I was making one drawer and I decided to use pre made drawer sides. I needed 2 3/4" high sides. So I bought a 6" tall piece and cut it down to size so I could have the finished top part. If I had used a 4" side and cut down I would have lost that. I used a spare piece as a Template for the dado cut height. I did not have to switch to a dado blade set(set of blades u stack together to cut wide slot in wood)because a simple two pass cut was enough for the drawer bottom.
I love to make stuff from old pallets. That said its not as easy as you think it might be. You can get pallets from just about anywhere and most places are HAPPY to give them to you. Some are made of junk and some are made from hardwood like oak. These are the one I like the most but also makes it harder to tear down. Here are a couple tips to help you tear these pieces of gold apart.
1. Tools: good claw hammer, 3footcrow bar, 1 foot crowbar, nail punch, gloves and safety glasses. This is the bare min.
2. Other tools. Zawsall, circular saw.
If all you care about are the cross pieces then you can cut the edges and then you only have to worry about the middle nails. If you want the joists then you need to use a saw to cut as close as you can on the cross pieces. Just take your time and before you know you have some great free wood and a pretty good workout too.