SPRINGFIELD — Although the city’s budget tops $1 billion this year, it is a frugal one that calls for negative growth in the small amount of funding which is considered discretionary.The City Council took its first crack at the $1.03 billion budget submitted by Mayor Domenic J. Sarno. The city’s finance department will continue meeting with department heads to discuss the spending plan and try to find ways to save taxpayers money at 5 p.m. Wedne…