Yep! it can cost a fortune if you're not careful.
I was wondering about WH Smith when I picked up a copy of Motorcycle Mechanics with a 1972 CB750K1 on the front page.
I had one back then brand new, I read the mag, emailed the editor asking for some help and he replied straight away. The editor at the time was the late Rod Gibson, his advice was to buy the best bike you can get as a starting point in order to have most of the parts readily available. Sound advice but my budget wouldn't allow me to do that so I down graded to a CB650Z that cost me 260 quid. Pics below.
The problem was that the bike was such a dog that I had to remove every nut and bolt and work from the ground up. The whole exercise cost me over £4,000 and I had to sell it on to recover my expences.
The danger is that you get so far in that you can't back out............