(Disclaimer: No medical training. Former analytical chemist.) Rapid test kits like these are your best bet if you want to go the DIY route. The only caveats I have are:
1) Unsure of the amount of blood required for this test. If it's just a pin prick you're fine, but if it requires a whole vial of blood, you will end up with some pretty nasty cuts trying to withdraw enough blood for the test.
2) Antibody tests such as these are inherently limited in their reliability. Not as reliable as the PCR tests, and that goes doubly so for these field litmus style tests. All it's really telling you is you how your body has reacted to potential exposures. A near-miss infection would show a false positive. It also takes time, so recent infections can give you a false negative.
3) If everyone on HN buys one of these because of this post, we will be depleting the available stock of these tests that could otherwise be used to save lives. Anything medical is going to be very scarce for the next several months, and we all need to do our part to help assuage the problem.