heroes even legendary

I fail to see how 1 gold per turn per champion bogs down an economy. At best one would obtain 7 champions, (5 more likely). 1 of these champions could be a commander which with the merchant skill provides +3 gildar per turn. Effectively removing the cost of 2 champions (assuming a decent amount of taxes).

Explain how the champions specifically are bogging down your economy? Might try raising taxes.

you can dismiss heroes the same way as any other troops you've trained. Click on the portrait of the hero, click on the two litte arrows in the action list reading "More Actions", click "Disband". You can also disband single troops and heroes when you open up the "Economy" tab in your Ledger when you click the "Govern" button to see an overview of all your troops.

And I agree with parrottmath that a 1 gildar upkeep cost for heroes is very reasonable, I myself would expect my sovereign to pay me for my services roaming the lands or sitting idly on my ass in a city's pub to decrease unrest.

even if you don't have an army to send along, you can still use excess champions to scout the map and pick up treasure chests (and sometimes also abandoned lairs when someone else lured the lair guardians out). with the loot you find there, they tend to make more money than they cost while providing a useful service to your faction (exploring the map). if you use them as army leaders and/or as combat units, you'll likely spend much more money on the wages of their armies and make more money from the monsters they defeat, so the 1g/turn is pretty irrelevant.