I see what your getting at, and part of the price view I have is based on purchasing power in the local economy, thus more properly local "credits" where Imperial credits represent purchasing power in the higher TL economy.
On second thought, I need to look at the conversion of credits. That is probably a better way to simulate what I'm thinking.
Further, the exponential scale should only be for manufactured goods. Also the scale should not be flipped for price reductions, still a linear scale there and a price increase eventually to reflect lost arts (e.g., making stone knies at TL8).
Also I'll admit my example is a bit extreme, TL4 is not a spacefaring culture, TL10 is. I'm thinking my exponential example really should be tied to the absolute TL. For example, selling a TL10 hovercar to a TL5 guy (that's about WWII?) should be pricey. Something TL13 to another starfaring TL10 culture not so much.
I also tend to make colonies that might be noted as a TL8 (to reflect local large scale industrial capability) not pay such a large price jump if they are from a TL10 world and know all about the repair and care of TL10 equipment. They might have a lot of TL10 equipment in a certian area, just not enough to be TL10 overall or be able to make it.
The exponential scale does certainly skew the economy (always a good reason to ditch it). But wouldn't that be the case at least for manufactured goods? Wouldn't a world with a 3 TL edge be able to make goods far cheaper given advances in manufacturing technology, labor costs being roughly equal (maybe a pretty big if)? What do low tech worlds have to offer? Labor, natural resources, unique biologics (e.g., from their rainforests, etc.), tourism, hand-crafts made by long forgotten low-TL techniques, art, music, land, tax shelters, professional services (e.g.: accounting), black markets, etc. Local industry might be able to compete on local TL products depending on the cost of shipping, trade barriers, tariffs, etc.
Analogies might be made to the 18th and 19th century. The Europeans could much more economically produce cloth, steel knives, and glass than lower TL peoples in other parts of the world. What they wanted was spices, bauxite, gold, cheap labor, etc. I'm not saying this trade was necessarily fair and free but its gives an example of the severe disadvantage lower TL worlds might be at.