Stay at the Boutique Poo Yai hotel in Chatuchak, it's only a short drive to DMK, 15km and in your budget.
Arrive in the afternoon, stroll across to Chatuchak markets and Big C afterwards.
The hotel has a great selection of guitars on the second floor, the hotel character.
https://www.guestreservations.com/boutique-poo-yai-ma-bp-place/booking?utm_source=google&utm_medium=cpc&utm_campaign=990032399&gad_source=1&gclid=Cj0KCQiAwOe8BhCCARIsAGKeD55xaNztC7p9A4fibD73cBAT1i8Z7jJyoN6v8WnrGRcpLdy8cbB1tSEaApKjEALw_wcB