The metalurgy for most any butted steel frame <$500 is going to be 4130 CrMo (Renyolds 520 and most tange tubes ARE 4130 CrMo) but differences such as seamed/seamless tubing, diameter, thickness, butting profile and cold-working the steel can result in significant differences even between CrMo tubes that all conform to the 4130 metalurgy spec. Additionally, further strength can be added by heat-treating steel (such as True Temper VS-HT, Tange Prestige, Reynolds 725). Even more advanced steel metalurgy (such as a stainless steel, columbus niobium or nivacrom, truetemper P3, reynolds 853, dedaccaia 18MCDV6) can be made into thinner tubes but will be above your pricepoint and is overkill for a commuter.