Hotels have government regulated prices (which should be listed in the rooms) but don't forget that these are the maximum prices allowed. It is not unusual to get rooms for a lower rate, especially out of the peak season (generally mid-summer and especially August) and if you are staying more than a few nights.
Hotels of lower category are simple but clean and almost always have an attached bathroom. Single rooms are not common so if you travel on your own you are likely to have to take a double room. Most hotels will however lower the price.
Prices for a double room start at around € 20 per night for low category hotels in cheap areas and go up to well above € 100 when you go to luxury hotels (of which there are not many and mostly on the north coast of Crete).
The price more or less determines the standard of the accommodation but will not necessarily be reflected in other important aspects such as the location (proximity of the beach, type of beach, whether it is quiet or right next to a road or a disco, ease of access and so on) so it is important to do your homework and find out that what you are booking is also what you want.
Many hotels in tourist resorts (especially on the north coast) are entirely in the hands of tour operators and can only be booked through them but there is still plenty of accommodation available for independent travelers.