Here is an example of a setup that starts off "cheap". HT inframe kit, less than $150. Beach cruiser from walmart, usually less than $100. Count the cost of tools you may need if you dont have them, maybe $50. But here is the problem. First, you'll need to add some better brakes. Thats $$. Then, some of the bike components might fail. Thats more $$$. Then, some of the kit components will definitely fail. More $$ again, Then, if the bike doesnt suit your needs power wise, upgrades. More $$ again. I should definitely know. I built two of these bikes, and between both of them probably dumped more than a few grand and countless hours of labor into them. Late last year, I decided to go custom. I don't have tough Montana winters to face (PA winters can be brutal, but the terrain is more forgiving here). I put a 98cc 4 stroke in-frame on a beach cruiser with motorcycle forks. I've got about $850 in this bike, and thats not counting parts that were given to me for free. The short answer to reliability for under $300? Not with all new parts and a new engine. I see that you posted about this engine that was given to you, and you already had most of the parts to make it work, so you saved a bundle versus building from scratch. i was thinking about those supports and wondering if it would be possible to drill holes and just bolt supports on instead of paying someone to weld them. Angle iron could easily be bolted on to the existing supports. A bike that can be driven daily through the long term and especially tough winters needs maintenance and quality components. If you were to build from scratch again, I'd not expect a bike to meet your needs for under $300.