Please just pay shipping.
I purchased a bed sensor and a chair sensor to build an alert system for my aging grandfather. I believe cost was $100 each. They were purchased from a company called telehealth. Unfortunately grandpa passed away before i even opened the box they were shipped in. If they could work for you, please have them.
P/N #BOS1130 BED Sensor
P/N #COS1111 Chair Senor
these are just the sensors. no other electronics. Was going to build my own.