You can go to the main square in town and hire a van or taxi for specific trips or just for the day. Be sure to negotiate! The bus service into Merida and back is excellent, and then you can take buses from there. You might want to rent a car for a few days, and use public transport for the rest. Read more about Progreso here: http://www.yucatantoday.com/destinations/eng-progreso.htm
Most monthly visitors to Progreso do not use cars, but rely on the local bus system. Frequent buses run from town to town.
They even have competing bus lines that run from Progreso to the neighbouring towns. The first photo is of the Combi's that run from Progreso to Chicxulub (the next town 5 km further east on the Gulf of Mexico). The second photo is where we flagged down the bus near our condo. All such rules are looser in Mexico. There are no bus stops - you flag down your bus.
In 2006, one-way prices for the Progreso to Chicxulub bus are 4 pesos, and for the Progreso to Merida bus are 12 pesos (I think it takes 45 minutes from the Progreso bus depot to the Merida bus depot).
The Merida bus depot is in the middle of a block. Don't forget to remember where the bus depot is (or you can ask at any of the tourist information places). You can also pick up the bus anywhere along it path just by flagging down the bus if it passes you on the street (as long as you are not immediately downtown -- it does not stop within about four blocks of downtown to reduce traffic tieups (coming or going)). We picked up the Progreso bus near Walmart in Merida a few times rather than walking back downtown.
We found the easiest way to get to Progreso from the east coast of Canada was to fly into Cancun, rent a vehicle and drive the 41/2 hours to Progreso, stopping along the way to have a meal. There are many rental agencies at the airport in Cancun and we chose Alamo. The service was efficient and the rentals reasonably priced.
Since our rental home was 11km from Progreso we needed the car evey time we went out. The road between Cancun and Progreso was excellent, as were all the roads around Progreso. The Mexican drivers in the Yucatan state were very polite and conscientious. Gas was a bargain compared to the east coast of Canada.
Bus is cheaper and you can get off at every block. If you have to take a taxi they are not too expensive. You can usually hunt one going down the road or meet one in central park. Ask the driver for a business card and then if you need to call him you can.