The lab I worked in used to have a Heathkit device that decoded the NIST radio time signal and output an ASCII string to set our time server before we switched to a GPS receiver. I doubt that you can find anything like the radio easily but someone might have one in a cupboard! It looks as if simple GPS devices might be quite cheap if $50-100 is in your budget. The commercial grade devices are rather more. Something that connects to a USB port would likely be cheaper than one with built-in networking but the latter would actually work as the time server. It's getting hard these days to buy the chips and build one.