Are the souvenirs for you or others you need to bring something home for...that can always be tough having a long list of people that you need to bring souvenirs.
As far as other people...I find buying packs of pens and then splitting them up among 5 or 6 people economical...also simple things like lollipops or tins of mints. If you are on
DDP or DxDP and have extra snack credits you can use them for the lollipops or other fun packaged snacks.
And as others have said postcards, note pads, key chains, etc. are all good souvenirs to bring to others.
If the souvenirs are for you then maybe you just give everyone a souvenir budget and let each person decide if they want multiple lesser priced items or one more expensive item.
Another great and non-expensive souvenir is collecting things from your trip like park maps, stickers CMS may give out. When young children ride the speedway in MK they give them a license, your KTTW card, a cheap $1 pen, some pictures...any little trinkets from the trip. A post card with your resort on it. And then when you get home you can go to a store like Michaels and get an inexpensive shadow box and then put all the little momentos from your trip in the shadow box and hang it up as a fun souvenir of a great trip. I made a shadowbox for my son's first trip to Disney and I think almost everything in it were free items we got on the trip...