The General Statutes of Connecticut (GSC) list the penalties for driving an unregistered car in CT as fines.
Section 14-12 of the GSC notes that a person commits an infraction if valid registration is not on a vehicle and it is driven on a public road. Failure to renew within 30 days receives a fine but operator's license shall not be affected. The exact wording of this section of CT law, titled Motor Vehicle Registration is as follows:
(a) No motor vehicle shall be operated or towed on any highway, except as otherwise expressly provided, unless it is registered with the commissioner, provided any motor vehicle may be towed for repairs or necessary work if it bears the markers of a licensed and registered dealer, manufacturer or repairer and provided any motor vehicle which is validly registered in another state may, for a period of sixty days following establishment by the owner of residence in this state, be operated on any highway without first being registered with the commissioner.
(1) a person commits an infraction if he registers a motor vehicle he does not own or if he operates, or allows the operation of, an unregistered motor vehicle on a public highway or (2) a resident of this state who operates a motor vehicle he owns with marker plates issued by another state shall be fined not less than one hundred fifty dollars nor more than three hundred dollars. If the owner of a motor vehicle previously registered on an annual or biennial basis, the registration of which expired not more than thirty days previously, operates or allows the operation of such a motor vehicle, he shall be fined the amount designated for the infraction of failure to renew a registration, but his right to retain his operator's license shall not be affected. No operator other than the owner shall be subject to penalty for the operation of such a previously registered motor vehicle.
So it appears the fine ranges from $150 to $300 for a vehicle being operated without proper registration.
CGS 14-215 lists another fine that you may also face for operation of a vehicle if the registration is refused, suspended or revoked. Here it states under subsection (a) that no person shall operate or cause to be operated any motor vehicle, the registration of which has been refused, suspended or revoked, or any motor vehicle, the right to operate which has been suspended or revoked.
Subsection (b) goes on to say that any person who violates any provision of subsection (a) shall, for a first offense, be fined not less than one hundred fifty dollars or more than two hundred dollars or imprisoned not more than ninety days, or be both fined and imprisoned, and, for any subsequent offense, shall be fined not less than two hundred dollars or more than six hundred dollars or imprisoned not more than one year, or be both fined and imprisoned.
To not be stopped by law enforcement, ticketed and have to face the penalties / fines associated with driving a car that is unregistered make sure you take the proper steps to register your car in Connecticut. The CT Department of Motor Vehicles should be able to walk you through the process.