Sometimes if a dahlia is a new introduction it will be high priced then get less from year to year after that. You're usually not getting a clump unless it specifies pot-tubers.
Check the suppliers list on the Colorado Dahlia for good suppliers that have a variety of dahlias & prices.
The Big List on the CDS site will tell you who have the dahlias you're looking for.

Here is a link that might be useful: Colorado Dahlia Society

I bought my dahlias last spring as flats of annuals. They produced wonderful tubers that I pulled up this week. I only paid flat price (36/$12). This seems SO cheap compared to the stuff you are talking about. Are they something different? They were plants about 12 inches tall, very bushy, soming in about a half dozen colors. They were beautiful. If these ARE the same as other types, why not always buy like this?

You bought border dahlias. The other ones are show dahlias- fully double blooms on 3-6' plants. Some have huge blooms-- up to 15" across & 12" deep. Look at the list & pick a grower/supplier- then look at their website to see the difference.