I commute on an old Czech Rapido folding bike. It's a Raleigh Twenty inspired model circa 1970's-80's. I need to replace the BB which is cottered. I figured I'd take this opportunity I'd upgrade to a cotterless system. I'd like to purchase the cheapest all-weather BB that would be reliable for daily commuting in wet weather. The bottom bracket shell is 68mm in width. I believe the threading is English. I really don't know many other details. I'd like to buy the bb and SS crank set for under $100. If it's cheaper to purchase double crank set then I'll go that route and put a bash guard on. Please help. Thanks.