Outta likes, what do you have for home improvement stores in your area? Lowe’s, Home Depot, menards? All of them probably have 4 packs of the led bulbs for probably $10 or less. They are a19 style, same type you would screw into lamp or light fixture in your home.
You just want to make sure you get them with removable diffuser and something like 5000k-6500k color temp for seedlings.