We just got back last week and our oldest is 9.5 (she turns 10 in July).
She *loved* the pick a pearl in Japan, and it's a really nice keepsake that she can always have to remember the trip so the price didn't bother me. The pick a pearl is $17 and the setting my daughter chose was $22. One thing to note, the necklace settings do NOT include the chain necklace. I wish I had known that ahead of time because I just couldn't bring myself to splurge on the extra $16 per chain (both of our daughters did it) since they are less at home.
Sorcerers of Magic Kingdom was a huge hit, she likes the Harry Potter stuff though so I guess maybe it depends on interests but if you ask her what her favorite park of MK was that is one of the first things she mentions.
She really wasn't too interested in the princesses, at least not like my 7 year old was, but she did enjoy getting autographs and she asks everyday if I've developed the pictures to add to her autograph book. You can get autograph books right at Disney in most shops for less than $10 that have the photo page on the other side of the autograph page.
She loved the pressed pennies, I printed off pages of what pressed pennies were where and she had fun looking at them and deciding which ones she wanted to get at the park we were going to that day.
She liked the kidcot stations more than I expected in Epcot.
She LOVED pin trading, and for a normally shy girl I liked how it really opened up conversation between her and some of the castmembers, especially the ones in the World Showcase that weren't from the US. She traded pins with a CM in Norway who was from Arandale (might have butchered the spelling, the kingdom where Anna and Elsa in Frozen where from) and she mentions that everytime when she is talking about them.
Rides will probably really depend, she is a thrill seeker like her mom and dad

she loved the bigger coasters. Big Thunder Mountain, Space Mountain, RNRollercoaster, Tower or Terror, Expedition Everest were some of her favorites.
She also loved the Animation Academy in Hollywood Studios, she is still practicing her Mickey/Minnie drawing skills in her spare time and if we had had time she wanted to go back for another class to learn a different character. She has always loved artistic/drawing stuff though.
Another thing to consider since you said it's a budget trip, 10 is the 'magic' age at Disney where you pay adult pricing for kids. This actually played a big factor for us in scheduling our trip when we did. We decided to go before she actually turned 10...so if you haven't solidified dates, maybe go the week of her birthday with her birthday being the last day or two? Then you are only paying the adult pricing on her for some of the trip.