I don't have access to real-time information about current prices of products. However, as of my knowledge cutoff in 2021, some of the cheapest 55 inch 4K Smart TVs available in the market were:
- TCL 55S405 55-Inch 4K Ultra HD Roku Smart LED TV
- Vizio D-Series D55-E0 55-Inch 4K Ultra HD Smart LED TV
- Hisense 55H8G 55-Inch 4K Ultra HD Android Smart LED TV
- Power Guard PG55F4K 55-Inch 4K Ultra HD Smart LED TV
- LG 55UK6300PUE 55-Inch 4K Ultra HD Smart LED TV
Please note that prices may have changed since then and that cheaper models may have been released. It's always a good idea to do your own research and compare prices and specifications to find the best deal.