I have tried the njoy 2.0. I'm pretty sure it's only 1 pound, last I checked.
Try this one- it seems to have a relatively narrow neck, and the 50 mm (2 in.) diameter weighs 2.47 pounds.
http://www.erosteel.com/shop/Classic-Butt-Plug.html?page=1
You can even get a detachable handle for it, which would add quite a bit more weight
http://www.erosteel.com/shop/Torch-Handle.html
Then there is a 2 in. max diameter version of the jewel plug, which weighs 2 pounds:
http://www.rosebuds.net/sex-shop/plug-jewellery/classic/cristal-xxl2/9-62
If you want to try a heavy plug with a wider neck, there is this one:
http://huse.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=HDC&Product_Code=218101&Category_Code=A3#.VS3csFzrtUQ
For a custom plug with a narrow neck as well as a narrow base, check this one out (pictured with a chastity cage, not included):
https://twitter.com/steelwerks/status/544662719174303744/photo/1
That one can be ordered from http://www.steelwerksextreme.com/butt-plugs
Now for e-stim- This seems to be the best option I have found:
http://shop.erostek.com/products/Intruder-Extreme-BiPolar-Buttplug.html
You can use a remote control for it:
http://shop.erostek.com/products/ET302R-Dual-Channel-Wireless-Remote-Power-Unit.html
* I am not affiliated with any of the above manufacturers or retailers.