Every EV novice seems to inherit the exact same pack of misconceptions about home charging, largely fueled by the dubious economy of using the travel unit as the daily home charger. I get you may be at sixes and sevens about the whole "EV thing" and are poised to return the EV to the lessor if it doesn't work out for you, so you want to make bare minimum investment in infrastructure. But you're mistaken. EVs are here to stay and it's silly to scrimp only to have a worse overall experience.
I will not be using both circuits at the same time as EV charge will be a scheduled one only at night/early morning hours.
It's one circuit. But the thing you're trying to do isn't allowed. That circuit is dedicated to range/oven per NEC 220.55. The EVSE requires a dedicated circuit per 625.40.
Generally, the idea of a "pinky promise" to be careful not to operate conflicting things at once is not recognized in NEC - e.g. the requirement for a generator interlock.
I am familiar with power-sharing devices but they are nearly $700 so I am looking for a lower cost code-compliant way.
Alright. See where you plan to put that box? Stick a Siemens 8-space subpanel instead. ($55) (does not work with a 4-space due to Siemens oddities with breaker spacing).
Two 50A breakers ($15 and $83 per you) in the subpanel with an $30 ECSBPK02 interlock between them. I'm picking Siemens brand because the ECSPBK01 interlock makes this easy. You can do the same thing with Square QO2DTI or Eaton CHML, but CH and QO panel lines are not cheap, and cheap is a parameter here.
You'll have to switch it manually but it's code legal. Hey, you wanted the cheapest rig possible. This is it.
I can purchase a 50A GFCI Siemens breaker for $83 - not a big deal.
Because your panel is Siemens legacy? Breakers don't cross-fit, even though they seem to.
The EVSE breaker will need to be GFCI, which is unfortunate, because it brings nothing to EV charging. But hey, you wanted the socket.
Oh, and long experience of the EV community is that the Leviton, Legrand and Eaton sockets (all the cheapies) tend to melt down under EV loads. the community universally recommends the $80-ish Hubbell or Bryant.
I am looking for a lower cost
One of my frustrations with the "money-scrimping" philosophy is that it seems to save so little. subpanels, Hubbell sockets, GFCI breakers... doesn't sound great.
I would run a plain, $15, 240V/20A breaker using 12/2 Romex (or whatever I had lying around) -- hardwired to a $450 Wallbox (CostCo). Yes, it's more. But not a lot more, and it will improve the experience all around. When nightly charging is easier, you'll charge nightly. Untangling that travel unit is a drag, and that encourages less frequent charging (which requires larger circuit).
4kW charge rate (20A circuit @ 240V) is plenty for home charging, and will provide 100-150 miles a night depending on the car and the night. Feel free to use fatter wire if your panel's Load Calc can support it.
And, because it's a Wallbox, I can add-on EVEMS load management, solar capture to export into the car rather than to the utility, or Power Sharing among multiple EVs.
