Getting bus to Taganga from all Colombia is cheap and very easy to catch at any moment. You rarely need to book, it is must of all in high season for Colombian people vacations (from the 27th of December to the 10 of January).
From all major cities of Colombia, buses offer excellent quality, are generally on time and are now the most common way of traveling in Colombia. For example, a tcket from Bogota to Santa Marta costs $220.000 pesos in 2023 anf from Medellin to Santa Marta around $235.000 pesos.
The main and faster companies are Expresso Brasilia, Copetran, Berlinas for getting by bus to Taganga from all Colombia. We use to recommend Berlinas because it is a family business, like Divanga Hostel (but bigger!!)
Their big buses include seats that you can lie down and travel sleeping in night bus.
Remember to cover yourself very well, they use the air conditioning very cold.