In real estate the value attributed to assembling a larger property is known as plottage. If each lot on a block was worth $100,000 by itself, but the 10 lots together in one block were worth $2 million, then the last holdout (assuming everyone else sold for $100,000) would now have a lot that was worth about a million to that developer. Of course if you get too greedy they might decide to just build around you.
https://ny.curbed.com/2013/4/8/10256168/the-two-little-townhouses-that-refused-to-sell-to-rockefeller You can probably back into what the developer can afford to pay on a per acre/per square foot basis. If you're asking more than that, unless they got some neighbors to sell for cheap it's not going to happen.
In rough numbers the land is usually about 1/4 of the value of the finished home. So a $300,000 house is probably going to be built on a $75,000 lot. This can vary greatly obviously if you're in a very expensive market where the land could be the majority of the final value of the residence. So if the developer can get say 5 lots per acre that's $375,000 per acre. Of course to build out the infrastructure to get those finished lots, plus the holding costs and risk, they need to acquire the land at maybe $100,000 - $200,000 per acre. Infrastructure costs typically run about $20,000 - $30,000 per lot but once again can vary greatly between small dense townhome lots or larger detached residential lots where there might be a lot more streets and utilities to install. So, if you aren't willing to sell for less than $300,000 per acre and the developer figures he can only sell lots in that location for $75,000 at 5 per acre, the deal isn't going to happen.