I found this great tutorial online for making DIY mercury glass, and I went to work with these products:
The glass pumpkin was a garage sale purchase for $1 (I believe the same exact one is available at Target for $4.99 currently). The Krylon looking glass spray paint is fantastic, but expensive. I found it at Michael's in the glass paint area for $11.99, but a 50% off coupon brought the cost down to $6. The silver, black and gold paints were about $1 each with coupons at Joann's.
I followed the tutorial from Lovely Little Details exactly, and my here is my end result:
The spray paint goes on the inside of the glass, so the mirror effect shines through. I did spray it on the exterior of the pumpkin stem, however.
Total cost for the project was $10, which was cheaper than the Pottery Barn version, for sure. Especially considering that I have lots of leftover supplies for future mercury glass projects!