While Autoslash has very good rates, it is geared at US consumers - their rates typically do not include CDW/LDW or SLI insurance, and one needs to buy that coverage at the rental car companies' inflated prices.
I would never recommend a foreigner without US auto insurance (or a premium credit card providing primary coverage, those are very rare outside of the US, though) to rent a car in the US without a fully comprehensive, zero-deductible, no-hassle insurance package.