Here a fixed IP costs 200 dollars a month, with a speed of 30/10 (those of 100/30 costs about 600 dollars per month per site).
A Dynamic IP 40 dollars with a connection speed of 120/30.

This company has a deposit and need to have a connection with it, so the technician before me
I run a VPN with two CISCO and DynDNS Routers. In general, it works fine but is obviously cut when the IP is renewed.
There is no possibility of switching to fixed IP costs.
But … I think the following and help me to discard it if it is not possible.

Can I replace the two CISCO router with PFSense machines?
I leave a drawing of the idea below but in principle we could hire two connections in each site.
Arrange two VPNs, one for each connection and with DynDNS. And then if one link falls I use the other to stay connected.

ThankYou!!!