It can be pretty comical (and impressive) to see what kind of clothes you can get at a thrift store for $5. Pick out outfits for each other (or for yourself) using no more than a pre-set budget ($5 is plenty), then wear the outfits to do one of the other date ideas (bowling, ice skating, etc)
If you know someone who likes guns, you can easily convince them to take you shooting. There are usually indoor shooting ranges if you live in a place where you don’t have an outdoor range nearby. You can take it one step farther and do some sort of “gun safety” class before shooting as part of the date.
Really old people love it if you come to visit them or to sing to them. They are full of amazing stories, and if they’re old enough, they won’t really care who you are or why you’re there they are just happy to see you! It will make you feel good, and give you lots to talk about.
Missionaries are always looking for help to do service, find people to teach or assitance with any of their volunteer activities. Get in touch with some and offer to help them — it’s very rewarding, and you can see what kind of person your date is!
This is another big hobby for a lot of people. Flying a model rocket can be done for under $20 (but obviously, some people get much more elaborate). If you are lucky enough to find an event, you can see hundreds of these of varying complexity. But if not, it’s still fun to pick up a starter kit at a hobby shop and build one together then fly it a few times.
If you don’t have access to a remote control airplane (I know I wouldn’t let you fly mine if you didn’t already know how!) you can go to mini-airports where enthusiasts gather all of the time to fly these things. It’s a pretty big hobby for some people, so it’s cool to see what they’ve done with it.
There’s a lot more in hot air ballooning than you would think (they’re harder to fly than an airplane) so it’s hard to get someone to take you up. But if you’re lucky, this can be a really fun adventure. If not, they have hot air balloon events where you can watch dozens of them take off at once.
Again, a date that’s probably more for the guy than the girl. You can buy all of the parts you need to build a potato gun for less than 20 bucks (ammunition included!) which is a couple of PVC pipes and an ignition source (like a lantern lighter and hairspray). Good fun — a decent potato gun will go 50 yards. You can find instructions all over the internet.
Rope swings can be great fun. Lots of lakes and rivers have already built rope swings (make sure they’re safe!) but you can build your own pretty easily. It’s especially fun if it’s in to water (you could do it when you go cliff diving)
Now that you’re older, you can probably engineer a really cool treehouse or fort. Wood isn’t TOO expensive, and if you already have the tools, you can make a pretty sweet club house either in your back yard or even out in the woods somewhere.