Die cuts are custom metal shapes designed for cutting paper (and other materials). Usually when you have a custom folder shape, they are made specifically for your project, so there is an additional charge. So custom folders are more expensive. But I say, make sure you get exactly what you want, even if you have to pay the additional expense.
There are many types of materials to use. Thousands of beautiful papers. Now there are a variety of inks to choose from. Folders can be embossed, printed with metallics. The sky is the limit. It really depends on how you and your designer choose to use your budget.
The inside pages should reflect the design and materials on the outside. You want the entire package to be cohesive down to the business card.
Folders are usually pretty expensive so there are a few ways to get the most of your budget. Go with higher runs. Low runs will run you $1 or more a piece, but if you get into the 1000, 2500 or 5,000 quantity range, you can really bring that number down significantly. What you need to do is get the most out of your higher runs. Do not put dated artwork on them.Also no contact information, that is for your business card. You want to put the minimum amount of words on them so that there is less chance you will need a reprint any time soon. I would suggest a nice full color folder with just a logo. And make sure you get the business card slits. That way when numbers, website or anything else changes, you won't have to get your folders printed, just your business cards. And those are cheap.