Actually, it would vary. If you're in Oregon, it's $2.3...
In Seattle, it's $5...
If you're a farm laborer (which is the kind of base level labor envisaged) it's still $1...
Which, I would tend to use the TCS or Striker tables to explain 'currency' differences for that sort of thing.
TCS for formal currency exchange, Striker for practical 'on the ground' per unit pricing, which would presumably factor in all the costs Free Traders don't deal in with getting an item through the supply/support/customs/taxation chain, and the desirability of higher tech over lower tech.
Those two tables have a LOT to talk about especially if you meld them together, but that's another thread.
Maybe Traveller retired characters go to low tech low port worlds to make that pension dollar stretch? Could live like a low tech poobah if those retirement benefits are denominated in hard CrImp.
I was under the impression that given the real world prices of the directly named gun examples in 1977, that somebody had figured out $3 = 1 Cr then.
So what is $3 of 1977 money then worth now, or more precisely how many current dollars to equate a credit given the previous 'exchange rate'?
My goto site for this is
https://www.measuringworth.com/
Using a simple price calculation of converting 1977 $3 into 2014 value, the answer would be $11.70 per credit.
Say it is $1 = 1 Cr. Then it's $3.91.
The website explains all manner of other ways to calculate this.
Of course T5 doesn't have to reference all that back rules history, but I would still use a similar approach, take a careful look at the price tags and equate them to current pricing for 'our' tech level items to get a feel.