Hello, and welcome to Just Answer!
Going by current prices on sites such as craigs list and eBay, a lovesac beanbag piece that seats 3 adults and is in good condition should sell for approximately $150 to $200. I suggest you price it at the high end of that range, as you can always come down in price but can't go up.
I hope this helps, but please let me know if you need more information regarding this.
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Yes, they are used. New ones are somewhat higher, as I'm sure you know.
If you will give me the measurements of your beanbag, I can narrow it down even further.
Thanks for the additional information.
Here is a link to a 6-foot Lovesac currently listed on eBay: CLICK HERE As you can see, the starting price is $200, and the Buy-It-Now price is $375.
I do think $150 to $200 is a reasonable price for yours. Are you thinking this may be too high or too low?