"I love that satisfaction of repairing something successfully !"
You just need to start looking at some new niche: In the last months I successfullly bought myself an iMac 24" "2009" for 150 Euro and an iBook Air 11" "2013" for 250 Euro. Both look like brand-new and are working flaw-less. The iMac is primarily used as a TV (I use IPTV streaming where the iMac is setup) and it was by far the cheapest option. As a bonus I got a whole Mac, too, which is still great for surfing, office, etc. The only thing broken was the magic mouse. After openening it (it is glued - arghh) and cleaning it, it works like a charm.
The iBook Air is just working. It has an Intel Core i5 processor and is super light. Perfect for trips or meetings (my "other" laptop is an 17" Asus ROG that weights like 5kg with PSU and stuff).
But even cheaper is to buy a broken iMac 24" or 27". They are pretty repairable, because the screen comes off (just hold by magnets instead of glue) and many regular PC components are used. And the screen is just fantastic. I imagine that you could get great deals on non-working units, where you just need to replace the HDD (regular 3.5" HDD), memory SDIMM (very available) or CPU (available and you could even upgrade to the fastest supported unit). If you have better equipment for BGA soldering, you might get your kicks out of repairing broken graphics adapters. The whole graphics board can be replaced, too. This means that by buying a few broken units, you will be able to repair a few, just by swapping components and cleaning the dust out of the interior.
This is just an example for a product that is sold quite cheap these days, but is still of great value for certain applications. I imagine they will get more expensive at some point, too.
Or why not consider buying a cheap X-Ray or Ultra-Sound machine? Mainstream is still not looking at these things. I have even started to consider buying a patient monitor for my own use (at least I would get propper heart rate, blood pressure and oxygen levels, compared to general public devices).
The point is: when everyone is into buying second hand test equipment to score a profit after an easy repair, try to find something else to give you the adrenaline rush (during repair) and endorphine release (after sucessfull repair).
Regards,
vitor