I highly recommend the lemongrass if you want a citrus-fragranced EO that sticks. Some people don't like lemongrass, but I really like it and so do some of my family, so that works out well for me. It is common enough that it is one of the lesser expensive EOs you can purchase and I often see it stores, although for larger quantities, I purchase online.
Peppermint and Spearmint are both strong scents that seem to stick and in my experience are not very expensive.
When you say herbs, what do you mean exactly? Fragrances that smell like herbs? Or actual herbs added to the soap. If the latter, don't expect you will end up with any herbal fragrance. You will likely end up with exfoliating soap from dried herbs, but not any fragrance. You can use herbal infusions in place of water for your lye solution, but no fragrance comes of it, and often very little color.
To evaluate herbal fragrances, I recommend you check out the scent bar at
The Vitamin Shoppe if you have one near you. They have a nice set up with their essential oils for customers to sniff, then 'cleanse the olfactory palate' via sniffing from a jar of coffee beans between sniffs. It's a very nice set up and you can find scents you might be interested in trying. Their EOs are not cheap, but after doing such a sniff test, I always feel obligated to buy a little something in the store that I might need, such as Bragg's Liquid Aminos, if not an actual bottle of EO.
You might find
this useful if you want to think of blends.