Mild steel is a pain to use and has low resale value. Its heavy, some wall thickness does not meet spec, takes longer to fit. Legal CM telescopes together so it can be sleeved and step down in size. The only real disadvantage of Moly to the home builder is that it must be Tig welded and not wire feed so your fitment must be exelint and not just close. Mild also moves around a bunch when welding, if you dont understand the welding sequince , it will be bent before you put the car together and in a dragster the motor to rear end aliginmet MUST be dead on;
You want a budget car, buy used, its around .35 on the dollar spent. Its gets you out there quickly and you will discover likes and dis-likes to help you plan on your next build. Two things to remember--- Get fully suited up and see if you fit (minor adjustments if needed) and make sure there is an SFI tag on it, the tag can be out of date which is fine because you know it still can be tagged