This app was mentioned in 2 comments, with an average of 3.00 upvotes
This app can give you a glimpse of the market, but you should expect to pay a little bit more since these are discounted prices. However it shows the location of motels which usually come in clusters like Sinchon area. If you can read Korean location names, you can find places in your desired area with that app. Booking is also possible, but that requires some knowledge of the language. https://play.google.com/store/apps/details?id=co.kr.yanolja.now