@defthand Re finger prick tests for ferritin or Vit D - there are highly reliable tests you can get, not from Amazon though! I regularly test this way and my results aren't all over the place as would happen if the tests weren't reliable.
Vitamin D: www.vitamindtest.org.uk/
For ferritin (in an iron panel, or included with other vitamins), I use either Medichecks or Blue Horizon. I do all my thyroid blood tests that way (my doctor accepts the results) as I'm a needle-phobe, and luckily I find I can do finger prick tests quite happily.
As for the Covid-19 antigen test, Blue Horizon are offering one for £149 but that's expensive and quite honestly I think it's a money-grabbing exercise. We shouldn't have to buy expensive kits! Testing needs to become far more widespread.