Prices in europe are cheaper with electric cars simple because governments don't tax them that much on everything and even subsidizes them. Petrol for your car isn't something that costs a lot of money, its the tax on it that costs a lot of money. U can bet we will see decrease in electric cars the moment it get taxed in the same way which it will the more adoption will take place. As they will want to have the same income either way.
That's the only reason we have people buying electric cars to start with, The same way why everybody bought a hybrid but never used the hybrid part because tax.
The cost depends on the government, not on the technology.
U can already see this happening currently with solar panels. I would make 11 euro's a month simple by having them on my roof so ordered a whole bunch of them because why not. However now delivering back with laws changing as more people get them on there roof which results in energy company's probably saw a massive reduction in energy consumption to the point they actually ahve to pay you, and lobby there way to the goverment that decide that rates are going down massively to the point its no longer worth it.
So what really changed here?, goverment. We got currently a 45-46% tax on petrol. U can bet when electric cars become the norm subsidizing is gone + 50% tax gets put on everything electricity.
Cheaper is only a thing when u are a niche, not when u are the majority.