I also wonder why everything is so expensive but to be onest, you will not find any of the components much cheaper out there.
For all small electronic parts, like DC/DC converter, sonar and so on, you will nearly pay the same in china but you must wait weeks to get them. Markus is a really reliable and fast supplier and I order regulary there for other projects.
You think the motors are too expensive? I agree with you, they are really expensive. But if you take a closer look and try to purchase the same or similar part, you never beat this price. I was looking for months to get a
motor like these for less, but I never found them.
You think the PCB is too expensive? Go and build your own, every plan and all schematics are available. But you will not be able to find a producer who create a single board for you for this price. You can build it on breadboards sure, but this is not comparable (I did at the beginning and it was a waste of time and money).
I also tried to order all PCB components (resistors, LEDs, capacitors) from a large electronic wholesaler. If i placed the order, I had to pay more.
Chassis could be less expensive if you cut them from HDPE plates or wood by yourself. Most of us don't have access to CNC mills, so we must use our padsaw. We will not be able to rebuild it that exact. If you try to purchase it from one of the CNC shops out there, again you pay much more if you order a single piece.
To sum up, if the whole package is too expensive, go and build your own from cheap materials (wood, chinese motors) or try to grab one of defect commercial mower available on eBay.
You really should buy at least PCB with needed components (approx 150€) as you will be unable to get it cheaper. But please also note, if you buy a defect mower (like I did) or buy motors and so from china to build your own chassis, it will cost at least 200€ in addition.
In my opinion, you will be unable to build a mower for much less than 400€.
You don't want to waste your time to build everything and you're just looking for a inexpensive robot, have a look to all these chinese lawn mowers. But bear in mind, they will also cost ~600€ at least but you will be unable to enhance them.
There is another project called Liam. They use ikea plastic boxes as chassis and cheap motors. But their mowers are much smaller and too light in my opinion. But if this project is too expensive for you, Liam might fit better to your requirements.
I agree to Dennis. I don't know how Markus is able to earn money with the shop and in my opinion, he don't do so.