Do you need a prescription to effectively treat toe fungus? Or do some OTC medicines work okay?

FDA. None of the OTC antifungals have formal FDA approval for treatment of onychomycosis. That being said, you can still use them. Lack of FDA approval does not mean they are dangerous to use; they just have not been studied enough in treatment of nail fungus. Personally, I find the success rate to be almost zero.
Foot fungus. Topical antifungals (otc or rx) work well. Apply product to entire foot & between toes 2x/day & continue treatment 2 weeks beyond visible clearance of infection. Keep feet dry with clean socks & powder if needed (fungus prefers moist environments). Treat insides of shoes with lysol or otc antifungal spray containing terbinafine. If persists 3+ wks or worsens despite treatment, see doctor.
Usually yes. Terbinafine is an antifungal medication that has a good track record for the most common nail infections. It is tolerated well, affordable and generally effective. There are other antifungal medications available as well. If deformed, painful enough surgery is sometimes performed. Lasers are a way to improve the appearance for a time of the fungal nail, but cost issues may be involved.