Just thought I'd share!
this is my Singlespeed. I commute on it. had it for 15 years and Will never sell it as powers everywhere.
i got Orange F5 alloy forks off ebay and the complete bike built up weights about 9kg. You can ignore the colour if you want..
I use an on one doofer on the back for the singlespeed conversion and it's smooth and doesn't feel like ther's too much drag, def less than a derailleur.
You can get a secondhand GT zaskar frame on ebay for about £185. Only draw back is that it wont take discs as is. Personally my V brakes will bring me to a skidding top in a meter wiht those tyre.
Don't think you can beat it for the money.