Depends on your pocketbook !
I did several BOM before, 2 were worth it and are beautiful quilts (but pricey even 8-9 yrs ago at $20-25 mo). The 3rd & LAST one I did from a different LQS, was a BIG disappointment ... directions & measurements were wrong, fabrics were very skimpy. The shop gave us more fabric, but I got tired of trying to "fix it" and gave it to a friend. It's still on her UFO shelf today Lol
IMHO the $5-10/free BOM are great, but the designer BOMs are MUCH more expensive than making your own quilts !

The LQS depend upon you buying something while they are there. That is how they make their money. On line stores do not have you in their stores buying other items. They have to make money on the monthly charges. If you are paying $500 for a BOM, not including backing, then you are paying too much. Shop around. You will find some that are cheaper.

I ordered the Civil War BOM from Keepsake last year. Yes, very expensive. I haven't sewn any of the blocks yet. It's my special project for when I retire or at least that's my story. Won't order such an expensive BOM again. Live and learn!

I agree that BOM's are more expensive than if you just bought the pattern and fabric yourself at your LQS, but the part I like about them is I only have to pay a small amount each month instead of a lot of money all at once. I'm still fairly new to quilting so I tried branching out by buying some BOM's. I'm doing one now that is called "Fundamentals" (???) and it costs $3.50 a week. Each week for a year they have sent me fabric and a pattern for a block that teaches me new tips and tricks. When I have all 52 blocks (for 52 weeks) I'll get a finishing kit to put it all together in a quilt. This has been a great "in-home" teacher for me! The closest quilt shop to me is an hour away so it's nice to see something online and have it delivered to my home each month. Maybe once I get my stash built up I'll feel different.