We need inexpensive gift ideas for high school graduates. S was invited to at least seven parties but does not want a party for himself. We were disappointed at first but will gladly put the party cash towards college expenses.
A card with $20.18 tucked inside.
I like @Middleman68 s idea. My daughter was invited to a lot of parties, mostly girls. I ordered an assortment of the classic teardrop earring from nickelandsuede.com while they were having a sale (so they ended up being about $22 each). Each time she goes to a party she can just pick a box, wrap it up and go. I’m still not sure what we are going to do for the boys parties that she is invited to.
A card with a $20 Amazon or Bed, Bath & Beyond gift card in it would always be welcome and is easy
A picture frame with a photo of their close group of friends in it.
Perhaps a keychain or a Swiss Army Knife for guys.
Cash. If you are uncomfortable with that, figure out where they are school and get a gift card to a restaurant or coffee shop near campus. My oldest just got home from his first year of college and was incredibly grateful for his Tim Horton’s and Five Guys gift cards. Side note: if they are at an urban school, you can also get Uber Giftcards. That was one of my son’s holiday gifts from his Aunt and he actually sent her a thank you every time he used it.
I love giving a Tervis tumbler for the school the student will be going to - they seem to cost around $15-$18 depending on the size. Bed Bath and Beyond often has them for the local schools and I just ordered one from Amazon for a friend whose child is going to a school that’s far away.
One other go-to gift (mostly for girls) is a notepad set with the name and school/class year - around $20 - “Jane Smith/Duke '22” (Full disclosure - I own a retail stationery business and do a lot of these for my customers. 
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We have had to gift so many grads through the years, and my D attended so many grad parties, it was a financial hardship for us to gift $20 to every grad. But my southern upbringing dictates that you bring a gift when you attend a party. So we buy the largest GIANT chocolate bar at the grocery store and put a pretty ribbon on it (NOT wrapped, just a ribbon). The grad (especially the boys) LOVE it, and if you are up for it, you can also write a small notecard and attach it to the bar.
For our nieces and nephews, and for close friends’ children, we do give a card with $20 cash.
Define " cheap" - cause, you know, CC… 
If you’re looking for less than $20.18 (which is a great idea no matter how many times it’s replicated)…
$10 Amazon gift card
TJ Maxx has so cute high quality spiral notebooks with a hard cover and quality paper for $5/less. My college D loves them. Attach a nice pen.
Many, many of Goskids’ friends went out of state for college. I bought 2x3 California flags for their dorm rooms…got lots of compliments from the recipients. And they were not expensive at all…
One of the best gifts my son got was a laundry bag in his school colors with his initials on it. I am not sure if they gave a different gift to the girls. Occasionally I have done a kind of dorm survival kit (bandaids, Tylenol, cough syrup, etc…) or an In-and-Out gift card.
Dictionary/Thesaurus set of books.
Why? That’s all online nowadays. Who needs more heavy books?
They come in very compact forms. Glad to read that the word “book” didn’t throw you. :)>-
Our circle of friends for both kids specified…NO GIFTS because really…some kids got invited to 20 or more parties. That’s a lot of gifts.
When we felt a gift was needed, we did a $10 bill…with a note saying…”enjoy a pizza on us”
My daughter is doing a photo of her and the friend whose party she’s going to in a nice frame.
Thanks so much everyone!! Your ideas have really helped!