Some launchers provide slots for standard-sized cubesats. This means that they can just carry some with them in a extra payload adapter for the cubes.
I am not aware that any launch provider has similar services for smallsats at your specs. Therefore, you would either have to deal with a rideshare or get your own rocket.
While a rideshare is cheaper than the entire rocket, you would most likely be the secondary payload (due to the small size and weight). That means that you can not specify the exact orbit. You can search for a rideshare opportunity to an SSO (Sun-Synchronous Orbit), but if the exact orbit isn't quite the same you'll have to compensate for that with your onboard propulsion system. Further, you usually have to keep up with or wait for the primary payloads timeschedule.
With you own rocket and therefore your sattelite beeing the primary payload, you have a few more options. You can determine your desired launchdate (which can still vary due to the launch provider), the exact orbit and your payload is the highest mission priority.
As you might have already guessed, that's where smallsat launchers come into play. If your sattelite is to fly on a Falcon 9, you're gonna pay the full rocket prize (usually between \$55M-\$62M). The theoretical price per kg is only applicable at full payload capacity. While smallsat launchers like the Electron have quite a high price per kg, this will be offset by the smaller overall payload capacity. Therefore, you'll pay only around \$6M for an entire electron rocket with a payload capacity of 150-225kg to a SSO. BTW: This results in ~\$27,000 to \$40,000 per kg.
In conclusion, I would say that price per kg numbers are mostly marketing numbers that can sound really impressive. For smaller payloads, rockets with higher price per kg can still be far cheaper.