About the cheapest that I've seen that I would trust in IMC is the
MGL.
That's about $800 for the sensor and $200 for the cockpit display. Add another $260 and get a remote compass too. For not too much more, the Dynon D6 has a full 6-pack of instruments and fits in a 80mm panel cut-out. I have actually flown that in IMC and it was rock solid. It can also have an internal battery that gives you 2 hours use if you have electrical failure.
The low cost solid state gyros are actually rate gyros, so need to be integrated to provide attitude data and this introduces drift errors that need fancy algorithms and additional input to correct. All this adds up to the cost of the budget instruments that I've mentioned.
But this technology is still developing thanks to the US experimental market that is allowed to use it in real IFR. So things will probably get better and cheaper.