I find workshops and trade are good for renown via artisan community, or buying fiefs if you grind that far, and that's about it. Changing the price of workshops would not change a thing for me - I'm not against it but either way I'm getting trade to exactly 125 for renown from caravans or workshops, and then ignoring it. Like smithing the gameplay of it is too barebones and grindy and only really serves to get one resource faster(renown for trade, money for smithing) via tedious and formulaic methods, so it's a chore not an enjoyable element of the gameplay.
I think trade needs workshops and caravans to generate high reward optional side quests with noteworthy rewards. The other workshop and caravan owners have issues with bandits or rivals or political obstacles that you can resolve, yours should too. Imagine using charm or roguery to manage political obstacles, or of course more straightforward combat to deal with any bandits or other criminals involved.