$2000 would go a long way toward building your own robomower.
Find a broken lawnmower in the trash for "bulk pickup" - free (getting it fixed might cost a bit of money, but in most cases, mowers get thrown away because the carb gets gunked up due to not being stored properly, or the air filter needs cleaning; ie cheap fixes).
Get the base or motors/wheels from an electric wheelchair (this might cost a bit of money, but should be doable for under $200 if you look carefully).
Various bits of steel, castors, bolts, etc - under $100.00 if you scrounge.
RasPi Zero W, GPS/IMU, sensors, etc (ie, electronics, sans motor controller) - $100.00, maybe a bit more.
Motor Controller - spend money on a good one, or money on the parts to build a good one. Probably looking at $200-500 dollars for a dual-motor controller. If you are really cheap, though, you can build a decent dual motor controller for the price of four 40 amp BOSCH relays, some wire, and one or two 40 amp DC SSRs; that'll get you a controller for well under $100.00, just don't expect great things from it.
The rest is up to you. Granted, that's the hard part, which may be worth the $2k depending on your skills, time, patience, etc.
Also, if you're confident enough in your coding skills to attach the code you wrote to a motorized vehicle with sharp, rapidly spinning blades attached to it.
Exactly, you can do a lot of amazing things with less money than certain things sell for. Most people spend that premium because the time required to build X for cheaper isn't worth it in the long run. (unless, like you said, its apart of someones interest or hobby)
When I was in college, I had more time than money, so it made sense to do these DIY things. Now that I have kids and a good income, I have more money than time, so I tend towards buying solutions to easily solvable problems. It sometimes makes me sad that I don't get to tinker, but I'd rather spend time with the kids.
Hopefully as they get older, we can combine spending time together and tinkering!
A couple of things you're missing:
1) Motivation. How many of these have you or anybody you know built and regularly use?
2) All the details. They require many skills, tools, experimentation, time, and spending of money.
As an example, I'm in the middle of a stalled project now where I want to make nice looking fishmouth pipe joints. I decided to cut them with a hole saw. But I don't have an electric drill that's slow enough so I've struggled doing it by hand and with a windscreen wiper motor, all the time wondering if it would be worth buying a drill press, but not the cheap ones from the home handyman shop because their minimum RPM is too high. I saw a cheap used one with no motor online so maybe I could somehow get an old washing machine motor and build some adapters to fit it together and buy an electronic controller - and that would be a whole new project in itself! What a lot of fiddly, costly details to "just weld some pipes together".
a friend and I were recording a song one day. I wondered why he wouldn't build himself a vocal booth. His reply was: "I'd like to record a song. If I were to start building a vocal booth, at the end of the day I wouldn't have a recorded song, but a vocal booth instead." Really made me reflect and become more mindful of goals and outcomes of my decisions and actions in work and life.
