That’s if you travel via Buquebus, you need to walk to Av. Colon to get a normally priced taxi.
There are fewer options at the Colonia terminal and the immediate neighbourhood is a bit grotty.
I just order an Uber. Usually I wait to order it until I clear immigration, but on my most recent trip a few weeks ago Argentina immigration took place before departing Colonia, so I ordered the Uber as I walked off the boat. Uber was 2.350 pesos from the terminal to La Boca, not worth it for me to walk to Av. Colon to maybe save a few hundred pesos.