I can't afford to be too patient, as I have a window when I will be back in the US (and most bozos won't ship internationally these days).

I scored a killer deal on a S6 headset for this build--- like $40 delivered (for a 'rare' 1" model)-- and some DT Revolution spokes at less than $1 /spoke delivered.... and a great stem for almost nothing. Chains and pedals are still OK--- but I really struggled with the drive train and seat post this round. I have built three bikes previously from all ebay parts. But seriously--- look at the percentage of professional sellers these days. My guess is that if you do a search of track or fixed gear, AT LEAST 80% of parts will be sold by pros. I wish ebay had a search filter to remove sellers by number of feedbacks--- so you could choose sellers with fewer than 200, for example (amateurs). These same pros are not selling at any sort of real discount.