Short answer — budget-friendly limited‑ingredient options (dog & cat) and how to save:

Cheapest common limited‑ingredient brands (examples with typical retail prices / per‑lb where available)

• Purina ONE (sensitive / “limited” / sensitive‑stomach lines) — one of the lowest cost limited/sensitive options: about $49.98 for a 31.1 lb bag (~$1.60–$1.70/lb at large retailers). (walmart.com)
• Blue Buffalo Basics (Basics = limited‑ingredient line) — often available in small test bags for ~$22–$24 and 20–24 lb bags around $50–$75 (roughly $2.0–$2.8/lb). Good mid‑budget LID pick when on sale. (target.com)
• Natural Balance L.I.D. (Limited Ingredient Diet) — widely available; small bags can be inexpensive (brand listings show ranges starting near $20) while larger bags commonly fall in the $48–$75 range depending on formula/size. (int2-sp-lb.petco.com)
• Merrick Limited Ingredient Diet — higher than the cheapest options; expect ~$26 for 4‑lb bags and ~$72–$76 for 22‑lb bags (so pricier per lb). (amazon.com)
• Nature’s Variety / Instinct LID — generally toward the expensive end of the LID category (example: ~ $80+ for a 20‑lb bag at many retailers). (petsmart.com)

Why prices vary and which to pick

• “Limited‑ingredient” is a label used across premium and midmarket brands. True LID formulas (one protein + minimal other ingredients) are often in the mid‑to‑premium price range; some budget lines marketed for “sensitive stomachs” (e.g., Purina’s sensitive formulas) can be cheaper while still being appropriate for mild sensitivities. (walmart.com)

Quick money‑saving tips

• Try a small bag first (4 lb) to see if your pet tolerates it — many LID brands sell small test sizes (cheaper up front). (target.com)
• Use subscribe/auto‑ship or repeat delivery discounts (many retailers offer % off first order and smaller ongoing discounts). (petco.com)
• Watch retailer sales, membership discounts, store coupons, and rebate apps (Chewy, Petco, PetSmart, Target, Walmart and Amazon often run promotions). (Examples above show typical sale/subscribe pricing across those retailers.) (petco.com)
• Consider switching to a less expensive LID within the same brand family (e.g., different protein or “healthy grains” vs. grain free) — formulas within a brand can vary substantially in price. (petco.com)

Safety note

• If your pet has true food allergies (itching, hives, ear infections, chronic GI problems), work with your veterinarian before switching foods or doing an elimination trial — some “cheaper” sensitive formulas may not help an animal with a diagnosed food allergy. For mild upset stomachs, an affordable sensitive/small‑ingredient formula may be OK as a first step. (If you want, I can list the lowest‑priced LID options available in the U.S. right now from specific retailers.)

If you want, I can:

• Pull current live prices (cheapest buys right now at Walmart, Chewy, Amazon, Petco, PetSmart and Target) and show per‑lb cost comparisons; or
• Narrow recommendations to dog only or cat only (and to wet vs dry).

Which would you like next?