Sealing cracks and sump covers alone rarely gets a home below the action level and is not a substitute for a system. Increasing ventilation helps marginally and costs you in heating. An active system is the only reliable fix.
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The honest answer is that the cheap options mostly do not work, and it is worth knowing why before spending money on them. Sealing is the most common DIY attempt. Caulking floor cracks, sealing the slab-to-wall joint, and covering a sump pit do reduce the paths soil gas takes. On their own they typically produce a modest reduction, not a fix, because the slab has more entry points than anyone can find and the pressure difference driving the gas is unchanged. Sealing is genuinely valuable as part of a system, where it lets the fan pull a stronger vacuum across the whole sub-slab area, which is why a proper install includes it. Ventilation dilutes rather than removes. Opening windows lowers a reading while they are open and it stops working the moment the house is closed up, which in this climate is most of the year. A heat recovery ventilator is a real product with real benefits, and as a radon strategy it is expensive per unit of reduction. The reason an active sub-slab depressurization system is the standard is that it reverses the pressure difference instead of fighting it. A fan draws soil gas from beneath the slab and discharges it above the roofline, so the soil under the house is at lower pressure than the basement and the gas has somewhere better to go than up through the floor. At $1,200 to $2,400 installed for a typical basement home in this market, the cost of doing it correctly once is close to what two rounds of partial measures cost. One local note on sealing. the mix of pre-war stock in the older Columbus neighborhoods, mid-century ranches in the inner suburbs, and large 1990s-onward subdivisions in the outer counties Older stone and block foundations in this market present far more entry area than a modern poured wall, which is exactly the case where sealing alone falls furthest short and where a two-suction-point system is the honest scope rather than an upsell.