Ouch. Well, I'm not sure what we're doing differently, precisely... you shouldn't need more than one or two Excavators? It's fine to have to build some, and it's not worth wasting your total coverage to delay building Excavators; due to order of operations, you need to build them before Scrubbers, and you'll probably need one, so you might want to build one with the initial starting budget.
I personally delay building greenhouses as late as possible, waiting until the verge of bankruptcy, and only in places where I won't build more scrubbers. I feel like that helps with getting the most out of greenhouse placement. Fun fact, if you have a single wind turbine in the middle of nowhere, the best coverage is to place 4 scrubbers above, below, left and right of it, then 3 greenhouses (1 line and 2 L pieces).
Otherwise, well, the game's hard to put into words. I recorded a video if it'll help. Although, maybe it's a puzzle you'd rather solve yourself? Up to you if you want to watch it! (Still uploading at the moment of writing.)