I would look at nurseries and big box stores fairly regularly. IME buying lilac too small is frustrating because until well established they tend to grow slowly. So if you want to fill up your hill, splurge a bit on the lilac and look for other plants inexpensively. Are you looking for suggestions of other plants? If so, what are your goals, such as scent, fall color, long season of bloom, etc.

Thank you NHbabs. I will definitely check out the big box stores. I'm looking for that super common light purple lilac that grows everywhere. I grew up in NH and I'm trying to find the one like my old house. It's probably still growing there!

As far as my plan goes, yesterday was a total moment of panic after clearing what I thought was a small space and it ended up being quite large. Fortunately, I will be dividing everything this year so I will fill it up with cone flowers, daisies, peonies, daylilies and irises. For shrubs I have a spice bush, roses of sharon, viburnum, and holly. I'll take a before picture. Right now it looks like a hurricane came through!

Consider putting down cardboard or several layers of newspaper or craft paper, water well, and then cover with arborists’ wood chips. I have gotten them by looking for line clearing crews in the neighborhood or a tree service taking down a tree and asking them to dump the chips at my house. Unless someone has asked first, they typically will do that because it is closer than the next nearest dump site. This will keep new weeds from sprouting and then when I want to plant I move aside the chips and cut a spot through the cardboard to allow for planting.

I've bought potted plants, including a lilac, at local plant sales in the spring that have been pretty inexpensive too. Problem is if you need a certain size or multiples that might not work for you. The lilac I bought was $10. but it was small. I did find a local plant sale I like and I go every year, but it's definitely hit or miss. You don't know what you will find from year to year, but I always find lots I'm looking for and at better prices than the stores.