I have seen & used a single-use ball/indenter type sensor, made by ("kip"? Swagelok?) but I think their pressure range is pretty high (1000's of psi). For lower pressures, you can try using burst disks, but the application doesn't sound like a good fit (I imagine gallons of foam spewing across your shop floor...).
Why can't you use a standard pressure transducer, with the port filled with appropriate fluid (silicon grease or oil or similar).