Before the day-by-day, there’s one tip that will save you the most money: eat like a local. Japan's convenience stores, such as 7-Eleven, Lawson, and FamilyMart, sell genuinely good onigiri, hot oden, sandwiches, and coffee from around ¥150, and they're located on almost every corner.
Local bakeries such as Donguri (famous for its chikuwa bread) do a filling breakfast or lunch for under ¥500. Save your yen for one standout Sapporo meal a day, whether that is a Susukino ramen or a Nijo Market seafood bowl, and cover the other meals cheaply so you can comfortably stay at the lower end of your daily budget.
Around Sapporo Station, the basement food halls of Daimaru Sapporo are another good option, with takeaway sushi, bento boxes, and local sweets that are easy to take back to your hotel.