I want to buy a hot knife but I have no idea how to look for a good quality inexpensive product. Any brand recommendations? and where do I buy one? How do I find out how many watt I need or what kind of blade is suitable? Mostly I will be cutting LW synthetics like cuben, silnylon, primaloft, supplex, velcro etc.

Any advice will be greatly appreciated.

None of the items you mention need to be cut with a hot knife.

If you want a hot knife anyway, benchmades are awesome

i would agree with Ayce. if your looking to get a hot knives to cut fabric they really work better with thicker fabrics.  I’ve got a bench top cutter box used for line, gross grain and zippers that I love Rochford supplies has some good prices on upholstery supplies but google works good too.

http://www.rochfordsupply.com/

JFF

For cutting Silnylon, cuben, etc. I would highly recommend a rotary cutter. OLFA makes quality products that last a long time and are still a good price.  You’ll need a cutting board as well which aren’t cheap but last a very long time.

http://www.olfa.com/RotaryCutters.aspx

Depending on the types of cuts you make you can buy different size cutters.  If all you do are long straight cuts you might start with the 45mm or 60mm cutter.  If you are making lots of curved cuts then I’d probably start with the 45mm or even go with the 28mm which will make even tighter curved cuts.