Remove unit from value

Hi there, I am pretty new to Grafana but like it a lot already. I am using it to display data from my solar system as well as iobroker. One of my devices is connected via mqtt ands delivers value with unit, e.g. 250.00VAR. For sure Grafana cannot handle this. My question: as I cannot modify the format of the device while delivery I have to modify it in grafana into something like 250.00. I tried regex but did not work. my data is stored with timestamp and the value. Can anybody advice if this modification is possible and show me the door to do so.