Ultimate cheap but sturdy safe bike is a all steel Huffy Cranbrook with fresh grease packed Bearings, Fenders removed or reinforced, a front drum, and a shock fork or monarch 2 springer as Agreen suggested cant be beat for the money. With Good lines, steel wheels, a decent rear brake, 12 gauge spokes, a steel frame and a 2 stroke can be done for 300.00-360.00 bucks total. There are great exact tutorials online for every step also. Yep steer clear of any Huffy with a rear rack welded on as they have weak spots above the welds and or below. But the Cranbrook is free of this problem. You could build 2 Bikes with this bike and system and have a third back up engine to boot for a 700.00 budget,Just saying. Welcome to the forum lots of valid but different Opinions here on bike platforms.
a 41 chain right away and avoid 90 percent of chain problems right away. Grind your clutch cover down using 2 doors tutorial also here