Can anyone supply a vendor name or brand name or possibly a web site that can supply low cost device's which can be installed permanently in a well casing top for close measurement monitoring of standing water within a well?
I don't know how far down you'll need to go, but there is a company called Erecta-Switch that has a variety of level sensors. A couple of other names are GEMS and Madison. These all have a variety of level sensing styles and may be a help.