I have bought from Adelman and Fina Gardens and Solaris Farms. Their prices are $16 and above but the roots usually are good size and produce flowers the following spring.

There does seem to be a big gap between even the big hybridizers on the same variety of peony. Southern Peony Blog writer actually did a spreadsheet on the difference in prices for Itoh peonies, I was shocked by the extreme difference. The growers she listed advertised the same size roots, too. I tend to search between several main growers, have a few that I absolutely prefer, but if the price is much different I'll buy from several different places. Fina is a favorite as is Hollingsworth and A&D. Fina had absolutely massive roots last year, it'll be interesting to see if they produce more flowers than typical for the 3-5 eye divisions sent by everyone else. Hollingsworth and A&D sent very nice divisions but their customer service is what sets them apart from the others selling similar sized roots.

The roots I received from Van Engelen this spring were not big enough to produce flowers this year, assume yours would be similar. The only time I've ever planted a bareroot peony in the spring and had a bloom the same season was one from Gilbert Wilde. Just luck there because it was a typical 3-5 eye division, no better or worse looking than the other 15 or so I planted at the same time. They have a rep for mis-labeling roots but I've never gotten a bad one from them and their prices are good, I put in at least 1 order from them every year.