Quantum computers pose a threat to current encryption schemes, as mentioned in this thread, somewhere in post-2030, but this date is being extended by doubling the length of keys used (RSA2K->RSA4K->RSA8K->RSA16K). Of course, fighting exponential growth (as expected, a Moore's Law equivalent for Qbits
is already presenting itself) with linear means will not last long (at most 1 or 2 doubling cycles, so 3-5 years, depending on just how fast the progress is), but it can allow current technology to remain effectively resistant for another half-a-decade, which is what we (the industry, and the rest of humanity, as an extension) are currently banking on.
Theoretical work on quantum-resistant (or even quantum-proof) cryptography has been undergoing for a long time.
Currently NIST is in the process of selecting its post-quantum recommendations, so we, as humanity, will have the capability to replace our cryptography with algorithms that remain valid even in the face of multi-mega-Qbit quantum computers. Some hardware vendors are already preempting this process and adopting some of these (or alternates) for their own security mechanisms.
What will be interesting is to see what kind of data that has been captured, stored, but could not be decrypted will become readable. Stuff that was encrypted 20 years ago may still have a lot of value (consider how many secrets and technologies are kept classified for dozens of years AFTER they were recorded). This will affect both things like national security, but also privacy, and has impact on the criminal underworld as well (depending on the statute of limitations for certain offenses where evidence may be encrypted).
As for this technology being accessible to the average joe: It will be. Heck, it already is. Log onto IBM's Quantum experience, put together a small quantum circuit and run it on one of their quantum computers. For free. Today. This is the foundation of Quantum-Computing-as-a-Service. Yes, the government will have access to the higher-end (read, higher Quantum Volume) systems first, but this is not going to be something that enterprises, academics, and even private citizens have no access to. This access is how companies intend to make money off this, after all.