Almost any repair tools, gardening, or anything NEEDED to DIY. You can do a lot of personal projects with very little money.
That being said, it's very easy to fall into a trap of going beyond what is needed into a full, fancy workshop, with all the shiny new equipment. If that's what you're goal is, that's fine. If you're doing it to save money, there's a lot of ways to just get the bare minimum, and be extremely effective. Especially if you can get used, or even non-functional equipment and fix it up yourself.
It's a tough balancing act. You don't want to dive all in and buy the nicest, fanciest, most expensive equipment right out. But also, if you buy too cheap, or too limiting, you're going to get discouraged.
Used is a really good balance between the two. Plan it out, figure out what you need, and meet someone locally to pick up their old stuff. Usually, if they're selling their starter equipment to upgrade, you can even chat with them about the hobby, and get some real good local advice. Maybe even and in with the local community.
And when it doubt, if it has a motor or needs to hold a heavy object over you then go for something in the middle range of cost unless you will be using is professionally or as frequently as a professional. The cheap stuff can be dangerous, and are generally not that much cheaper than a decent home use tool.
Estate sales and garage sales are other places to pick up used tools if you have a rough idea of what to look for like the finishing touches that used to be put on older higher quality tools like smoothing mold lines. Old mismatched tools from formerly reliable brands like Craftsman can be had for cheap!
I had to talk myself out of looking at small backhoes or tractors with a backhoe attachment today…. because I’m thinking about installing a single French drain. My “land” is 50’x100’, in a city.
Going big instead of being reasonable is a very real affliction that affects way more people than you realize.
If I know I only need a tool once or twice, I always buy Harbor-Freight (discount power tools if you're not familiar with them). I've always been able to complete the job with it, and anything beyond that is just bonus IMO (versus renting a better tool for the job at equal or greater cost).
Normally, though, they last a lot longer than that. I bought a HF drill in like 2004 and it finally died last year and was used pretty heavily throughout its life. Pretty sure I got my $18 worth.
They always sale descent mechanics tool sets for like $100 on black Friday and sometimes other times from home depot or Lowes.
That and youtube will pay for itself the first time you need to do an easy diy job on your car.
Why pay a shop $300 dollars to replace a thermostat when you can do it for a $15 part and $20 of radiator fluid yourself?
$30 set of jack stands and you'll never have to pay a shop $400 again to replace your front brakes. Good brake pads are $50.
Spark plugs need replaced? $200 at a shop for a 4 cylinder car, or do it yourself in under an hour for $35 worth of spark plugs.
There's tons of vehicle stuff that's not very hard to do that will save you tons of money with a set of tools and the ability to learn. I drive 15+ year old vehicles and have only taken one to a shop twice in the past 20 years. I do stuff a lot more advanced than your average person probably wants to try to do themselves, but I like working on my own stuff. But most of what I do is easy enough for most people to do without being too difficult.