Welder extension cord

Hi all, I would like advise on how to make a 50 ft. extension cord for a 175 (max amp) MiG welder it draws about 20 amps at full output. I know they have them on ebay and other sites but they are $100 plus. Anyone make up their own ? If so, how much did it cost you ? I want to plug it into my 40 amp dryer circuit so I would have to replace the plug anyway if I bought the pre made version so I would rather make something up If I can without sacrificing safety. I need to get out to the driveway with the welder so even if I ran a dedicated circuit the receptacle still won't be near the driveway and I would still need an extension just not as long. BTW It's my first welder. Thanks in advance.

I made one up with, I think, 8/3 wire and bought the male and female ends at Home Despot. It still cost a fair amount in the end. I think for 8/3 wire and the ends it might cost you in the $100 range anyway, but the cost of copper drives the wire cost and I dunno where it is right now.

Before I bought my generator cord I checked Northern Tool and HD and the prices on wire and plug ends ($80+) were 2 -3x as much as buying on ebay. Ended up getting a new one off ebay for $27 and free shipping.

Thanks guys, So I guess there's not much savings by making it myself. Guess I'll keep an eye on craigslist for some 8 gage wire. Maybe I'll get lucky.

Try an R/V supply store ... they carry some heavy-duty cords. Would that be heavy enough?

Thanks Spot, Perfect and for half the price.