If you were in the US, I might recommend “the art of server” ebay store. Even outside, check out his youtube channel; it has awesome stuff, little things like flashing raid cards to hba mode.
HBA:
I use a couple of cards like this, flashed to IT mode:
If they are still available, around £30 each is a good price in my book, your mileage may vary. You might be able to even use it without flashing, but I only use software raid anyway, so flashed it.
If looking on eBay, I would look at the ibm m1015, which is like the same card, but might have a better heatsink. not sure on that.
there are a few re-branded LSI cards which are basically the same, but some are on slower buses (pcie gen1 and gen2, so double check the listing. I think this one is gen 3, but the ones I have are gen2, so need all 8 pcie lanes for speed. Gen3 would probably work in a gen3x4 lane slot
there are a few advertised on ebay with p20 firmware, and zfs advertised, so a fair amount to look at.
For networking:
There doesn’t seem to be the number of cards and deals as there was when I got mine; it could be there was a shift in the industry up to 40gb, and a load of shops were shedding old kit; I got 4 chelsio nic’s from china off ebay, and I’m sure I didn’t pay more than £35 per card, but looks like the good times are not around anymore. (sorry)
You could google this and see if it will work in your system? I have no idea
and maybe look for similar elsewhere; it seems BH is limited in stock with nics for a good price, a lot of their stuff is expensive, but there is not a lot better on Ebay.
Switches:
Better off getting one of those 4 or 5 port ones that have been bandied around recently for about £250 or whatever, with 4 SFP+ ports, and maybe some sfp+ to 8p8c (rj45) transceivers for non 10gig machines:
MikroTik CRS305-1G-4S+IN
like this, but I don’t know best source:
Overall, I would not worry aobut getting stuff off Ebay, even with simple packaging, a lot of stuff does work.
There are probably scammers out there, and people who just post phone books, I don’t know.
There must be European sellers of refurbished stuff, I haven’t really looked.
Maybe Victor Bart from Youtube might have a source? Or MyPlayhouse channel, both are euro home-labbers.
Otherwise there are a few here who gather electronics