What option do you think is better?

Some people consider the d4 as a bad dice. It doesn't roll that well etc.
You might like to consider the d8 as well.
11223344 or
11122334 are examples that you can use.

Then again, with 2d6 you can easily have 4 EQUAL options.
1-3/1-3 is A
1-3/4-6 is B
4-6/1-3 is C
4-6/4-6 is D
Which requires 2 colours. But the pips can remain at default.

Or simply sum them up, if you don't want different coloured of d6. But still 4 EQUAL options.
A: 4 or 7
B: 5 or 6
C: 8 or 9
D: 2, 3, 10, 11 or 12

Another thought occured to me.

Having just one d6.
A: 1
B: 2
C: 3
D: 4
A or B: 5
C or D: 6

High rolls allow the player to choose out of 2 options.

Just wanted mention that dragon wood uses 122334 dice.

Absolutely 2 standard d6 is cheaper than one custom d6, though it's largely the upfront tooling cost and very minimal from my experience.

My latest custom d6 quote included standard d6 as well. at only 500 copies the standard d6 are 8 cents each. The custom are 8 cents each plus a 200 tooling cost (making them just over 9 cents a piece at 500 games (15 dice per game)).

Obviously the more you make the cheaper it is per die as well (both custom and standard).

I think the problem (if you want to call it that), more so than cost, with rolling 2 standard dice in Elkobold's suggestion is that you then add in the extra thinking step (math). People tend to dislike having to consciously do math to get a needed result.

A custom D6 shouldn't be a huge extra expense, but it's also not nothing. If you're going that way, you probably want special art printed on it, not just pips (my game has custom dice but just regular pips on any given face). Though I'll also note that some manufacturers might give you a deal if you just have regular pips on the sides, since there's no art setup cost for art they already have. That's not for engraving, of course.. just for printing. I'm looking at $0.10 per custom die for my game, MOQ 1000.

Could a spinner be an option?

I remembered that Deep Sea Adventure uses 122334 die as well as Dragon Wood.

https://boardgamegeek.com/boardgame/169654/deep-sea-adventure

So I decided to do some research on 122334 dice. It turns out this die is half of a Sicherman dice set. The die in this set is 134568. Together they produce the exact probability spread as 2 standard d6s.

https://en.wikipedia.org/wiki/Sicherman_dice

Though it was a fascinating tangent to explore it did not really help MAR. I found some places to buy a Sicherman dice set online, but I couldn't really find a way to get them in bulk. So if you decide to use this type of die there may be a mold for it somewhere.