Dog-cheap is an idiom that means very inexpensive or cheap. However, if you want to convey the same message but in a different way, you can use several synonyms for this word. "Inexpensive" is a great synonym that is widely used and can be substituted for dog-cheap. "Affordable" is another option that conveys the same meaning. If you want to sound a bit more formal, you can use the word "economical". Other synonyms that are similar include "low-cost", "reasonable", "bargain" and "inexpensive". You can use these words interchangeably with dog-cheap to add more variety to your writing and speech.