Repairs cost money too. Spare parts cost money, and tools cost money too. You can end up spending the same amount on repairing an old thinkpad as buying a new laptop (probably not a new thinkpad though).
Quite true, especially if you buy a relatively expensive used Thinkpad, have considerable repairs on it, and compare the total cost to one of the new "other brands". To some extent, luck is involved, just like when you buy a used car. But it helps to be knowledgeable, although that generally requires experience - and you pay for that too.
If your cash situation isn't great you might want to buy a new one since it is less risky than buying an old one. I am a student and I tried getting used laptops to save money, but in the end I got a load of rubbish, and lost money.
I can commiserate. My first Thinkpad was a grossly overpriced 765D on Ebay, where the seller misrepresented the CPU as 266MHz (it's really 166MHz) and lied when I asked specifically. He was later excluded from Ebay for multiple misrepresentations and even later convicted for fraud.
This first bad experience, however, was partly my own fault, as I hadn't realized how confused the Thinkpad model designations are (why is a 765 less powerful and older than a 600?), and how important - and difficult - it is to find out exactly what is in a specific model (CPU, HDD, display, periphery).
In the meantime I have around 10-12 Thinkpads of various types, the newest two being T21s, and have generally paid less than EUR 50 for them (EUR 100 and EUR 65 for the T21s). The learning curve helps to make fewer mistakes as you go on, and all in all I still have only spent about the same money for my whole "collection" as I would have for one new "other brand" laptop.
My situation is different from yours, however, since this is a hobby for me and I'm not dependent on the Thinkpads for my work (I use a desktop machine for that).