Here are some records which show a larger picture. It is not so simple as merely Southern exports of goods vs Northern exports of goods. Add in specie (gold and silver), which has to count, the balance for 1859 is much closer:
South 198 (rounded off) millions Non-South (rounded off) 135 millions.
Now add in contributions from immigrants (who brought money from overseas to the USA), which counts against exports, which was at least a few million dollars, mostly in non-south areas, and earning from services rendered overseas by US companies (most shipping) another few million (mostly from the North) and you are coming up with pretty near parity in non-South and South contributions to the balance of payments.
There are more complexities, of course. Many of the immigrants sent money back to Europe; money was invested (mostly by the British) in American companies, particularly railroads, mostly in the North. Loans were made from abroad to people in the US. Those may have been more in the South.
The balance of payments was not perfect, but bounced up and down from year to year. 1859 was a pretty high year for Southern exports, but also for export of gold and silver.
It is obvious the South was not being financially destroyed by the North. Some in the South may have thought so.
A serious problem for the South was the industrial revolution was undercutting the economic viability of slavery. A lot of people at the time could see a slave based economy would not be viable in the future. That undercut the entire slave owning culture of the South.
Gold and Silver came from mostly Nevada and California, and it is misleading to count them as the "North's" contribution.
Specie is not trade. Nations are loath to part with Specie and won't do it unless they have no choice.
Specie is not "trade", trade is "trade", and it was clearly in the South's best interest to get away from Northern laws taxing them at 12 times the per capita taxation of the Northern population.
Remaining in the Union made no money for the South, and caused them all sorts of problems. Leaving the Union would have gotten them an immediate 65 million per year taken out of Washington DC's coffers and put into Southern enterprises and infrastructure.
The swapping of Charleston for New York as the financial center would have netted them more still. The capitalization of their much smaller population would have had a massive effect on their economy.
You don't see the financial threat that the South posed to the entrenched powers in the North. You've never thought along those lines because no one pointed out to you the financial situation.
Nobody ponders how much of a money losing situation (for them) was Southern membership in the Union.