For staying safe you want high max range and energy-compensated dose response. No ultra cheap devices offer that, mine is the closest thing on the low end of price, but consider me biased... If anyone finds something to contradict that feel free to share, because it would be new info to me. Then there is the second hand market, for example mrad 113 is a good device that can sometimes be had for a reasonable price, probably there are other pro grade dosimeters on ebay for a reasonable price but I don't know follow that market closely.