Exactly.
You see, there are two things in the tech trade mechanism. First, you can get shop around for techs and get maybe 5-6 techs for your single one, and second, you have a source of money throughout the game. Question is, which is the biggest evil, so to say.
That's because of some of the base mechanics of RFC type mods.
Civs have different production and research modifiers. On top of that, number of cities is also a huge contibutor to the number of beakers needed for a tech.
A given tech can cost multiple times as much with a big empire than it would with only 1-2 cities.
So in the beginning (right after your spawn, when you are very small) it's unavoidable that you can get way too good tech trades. Later, when you have a decent sized civ, you will have a much harder time to get a fair trade.
That's also the reason a small AI civ and a big AI civ values the very same tech on very different levels.
For example AI Byzantium will usually give you whatever it has for a new tech. They usually have much more cities than you in the early game, on top off that they have the worst production modifiers.
While these are certanily not gamebreaking, they can get somewhat annoying, and they provide a fairly big advantage to the experienced human player.
And I don't really see a solution without getting rid of the tech trade system (which is very immerson breaking anyway IMO, even without looking at these issues).
I would much rather have a tech diffusion system, similarly to the one we have in Realim Invictus. So you can get various discounts on your techs based on it's availabilty in your neighbours / civs you have a trade agreement with / the global average.
That also has it's problems, but probably would be much better.
Could it be (potentially) coded so that you only can buy a half of a tech, and the other half you have to research yourself anyway?
Could it be done so that, mathematically speaking, the tech trade and money trade exist in different spaces, so you only can trade tech for tech and not for money?
Neither of this is solvable, not without rewriting the whole diplo trade system.
What concerns that old funny guy in Rome, is another thing. I'd say, strip him off all of his money and techs. He's there only for building churches and chewing gum.
Yeah, I already disabled tech trade with the Papal States, will be up with the next commit.