Charter Spectrum → [HSI] Back up Connection help

So I am okay with computers but not a pro so I will try and word my question as best as possible.

I have cable internet through Charter but I have POTS through the local phone company. $9.99 for just a dial tone couldn't give that up even with the taxes and fees its cheaper than charter.

No on to my main question I am looking for a fail back up to my Charter connection should it crash. I wanted to know if I sign up for one of those netzero or something free dial up plans is there something I can do to my main computer that will auto sense hey we lost connection and auto dial out to the back up dial up ISP?

I run a hourly reporting weather station that needs to be online 24/7 so I was wanting to know is it possible to set up a fail safe back up to dial out should charter crash?

There are routers that can do this. They are usually expensive.

There are dual WAN routers available that could easily accomplish this task but none that I'm aware of (consumer grade) that will handle a 56k modem as a backup. Assuming you had cellular phones you could probably add a USB modem to your plan for $15-20/mo and have cellular backup with a Cradlepoint among many other options. A cheap DSL account would be good too, assuming availability.

Since it sounds like the software runs on your PC you could install a modem then set the machine to dial whenever a connection is not available. The issue you may find is that it probably wouldn't fail back to your Charter service automatically, and would likely keep the phone line tied up until you disconnected.

Here's what I would do for the cheapest solution (kind of dirty but would work, and will require a bit of technical know-how...not the best but is probably cheapest):

If your weather station is a PC, I would write a scheduled task to check the connection (however often you want...say 10 mins or so) and then dial out if you can't connect. You can use rasphone command line tool to execute a dialup connection.

In english, it would be something like:

Ping x.x.x.x from source ip (ip of your nic)
If successful, disconnect from dialup connection if active using rasphone.
If failure, dialup connection using rasphone.

In powershell, you could use something like this code below (note this is rough and would need to be adjusted):

if (Test-Connection -Source Your_NIC_IP_Address -ComputerName IP_TO_PING_TEST_AGAINST)
{
#Connection via NIC is OK, silently disconnect dial-up if active
Start-Process "C:\Windows\System32\rasphone.exe" -ArgumentList "-h NAME_OF_DIALUP_CONNECTION_IN_PHONEBOOK"
}
else
{
#Connection via NIC failed, silently dial-up.
Start-Process "C:\Windows\System32\rasphone.exe" -ArgumentList "-d NAME_OF_DIALUP_CONNECTION_IN_PHONEBOOK"
}

I use my smartphone's tethering as my charter backup. If you can't tether or hot-spot with your phone, get a freedompop hotspot. It's pretty inexpensive to purchase and free to use if you're careful. It will be way faster than a dial-up modem.