Short answer: Tokyo's reputation as expensive is overblown for budget travelers. $1 onigiri + $4 sushi + $1 metro = real prices.
Tokyo is mid-tier on TenDollarPick at $3 base. Cheap wins: 7-Eleven onigiri ($1.50), conveyor-belt sushi ($4 meals), free temple/shrine visits, metro day pass ($5). Catches: nightlife and Western food are premium. Budget backpacker can survive $30-50/day. See full Tokyo guide.