Going for nathan stuff would be a waste of money because your thumb will stay unprotected.

There are several cheap solutions. Use what you've got and go DIY to increase warmth for a few bucks

There are some overmitts that would get you the outershell for pretty cheap. The problem would be the lack of breathability of those waterproof one
overmitts | eBay
http://www.amazon.co.uk/gp/product/B...=1&*entries*=0
and

simply put those overmitts over your gloves

and/or
you could combine those overmitts with some ragg wool gloves or mitten
Results for "mitts" at REI
dachstein mitts (top quality)
http://www.sweatersintl.com/woolmittens.html

You could also DIY some handlebar mitts

Another option could be to go for snowmobile and ski mitten
-scott hyland mitts (palm made of clarino which is a synthetic leather)
Men snowmobile hyland mitts - ADM Sport (CAD$)

-coldwave sno fire 3 mitts (don't expect amazing quality for the price)
Men snowmobile sno-fire 3 mitts - ADM Sport (CAD $)
COLDWAVE SNO FIRE 3 FINGER MITT (on sale for less than 32$ US)
Coldwave Snow Gloves for Men - Motorcycle Superstore (CAD $)

-castle X platform mitts (don't expect amazing quality for the price)
CASTLE X PLATFORM Mitt

-kombi Storm Cuff II Mitt
http://shop.mukluks.com/Head-Hand-Gear/products/60/

-Thrift stores and army surplus

-Outnorth has some hestra products on sale
http://www.outnorth.com