Hi! it's great you opened up a shop to help others find villagers~ I took a look at it, and based on experience I can say that it's best to start off with affordable TBT prices, then go up little by little as time goes by. Demand for certain villagers really tends to go up and down, but if you know which villagers are most popular then I'd say somewhere between 60 - 80 TBT is ideal. Villagers that are not so popular but are still sought after, I'd say 20 - 40 TBT is good. But really, a shop owner can set prices to whatever they want. These are just the prices that have worked for me thus far
if you'd like, you can compare prices at other active shops, or wait until your first order and negotiate what sort of price they are most comfortable paying, and go from there.
I recommended adjusting the price of villagers with no Amiibo to at least 100+ TBT because they are much harder to find and obtain, especially if they are original (meaning they have never been giving a gift and their clothes/catchphrase have never been changed)
Hope this helps! I wish you the very best with your new shop!