Not only does it depend on area on the Sout Shore but many times it depends on the street that it it on , i.e. You can be in Great Kills and there is a big difference now between below the Blvd. and bove the Blvd.
When appraising a home there are other criteria taken into consideration, such as what Town in South Shore, 1 of 2 family, condition, basement, number of beds, garage, house square footage, etc. Feel free to search MLS on my site and Register your email for sold comps.
Keep in mind that square footage costs do vary, and doesn't account for location and other considerations; therefore, it's really in your best interest to also review closed recently sold similar properties in the immediate area, and their final sales price; your agent can provide comps.