I went to Wikipedia to get some basic facts.

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

The 12 Amendment occurred in 1804. Before that, the electors were to meet at a "Continental Congress," which was held in different cities ( and not Washington DC).

From the wiki article, the 12th amendment mostly addressed the problem of the president and vice-president not getting along because of differing partisan interests.

I could not find how the electors were elected in the wiki article. I assume that legislatures did the electing after the 12th amendment. The change to the legislatures only approving whoever won the majority vote of the eligible voters came later.

The 12th amendment moved the actual election from the continental congress to each state legislature. So the electors did not have to travel. Reading between the lines, the electors were no longer free agents in casting their vote for president: they were tied to partisan interests.

Also the viable candidates for president were known, so the electors chose only one of those known contenders.

Keeping the electors away from each other meant no surprises could come from a national convention of electors. Their only choices were the proffered slates.

To me, it seems cost prohibitions are a moot point. The founding fathers found the means to travel to do politics before (i.e., they were rich and had servants/slaves to keep their businesses running). There's no reason to assume the electors could not have taken a few weeks off. Besides Congress was already travelling, incurring great expenses, which may or may not have been paid by the federal government at that time. The electors convention (for a few weeks every four years) would have been a much smaller cost than Congress.

The original intent of the electors, who were supposed to the wisest of the state legislators, was seriously watered after the 12th amendment. And maybe that's when the whole process to elect the president became byzantine.