>could not compete against illegal imports
How could that be possible? Imports had to be made in hard currency which was incredibly scarce in the Soviet Bloc (a VCR cost couple years of engineer's income on a black market), and was hard to obtain both for official/communist enterprises, and private individuals. Locally made stuff was bound to be a lot cheaper.
At least in Poland it was semi-common that if you had any family abroad they could send you dollars. So yeah a soviet computer was in theory cheaper but it was impossible to buy, or you could just walk into PEWEX and walk out with an actual commodore 64 bought with dollars that you "happened" to have. Of course, PEWEX stores were fully state-sanctioned enterprises, not illegal imports.
> Locally made stuff was bound to be a lot cheaper.
Lots of stuff under communism was cheaper on paper. It was also extremely crappy and/or unavailable.
So black markets were thriving, even though, as you rightly point out, used hard to get, expensive currency.
Yes, but, wasn't the prices fixed for stuff? I imagine there must have been things which were either cheap to buy, or which could easily "disappear" from a production line and sold in the West for more than it was worth on the other side of the curtain.