Here's another idea.
You should have several technology trees, You should have a Technology tree for everything for example.
- Vehicles
- Machinery
- Climbing Equipment
- Lowering & Rigging
And so fourth.
Each technology tree should have sub categories in them for Example.
Click Technology Trees.
Click Machinery
Then you will have the sub categories with say the top 5-6 leading Machinery Brands in the industry so Husqvarna, Stihl, Viking which ever you see fit.
Once you click on the desired Brand you have and entire technology tree from basic to specialized.
So the first Chainsaw you can buy in the Stihl Sub category will be Stihl MS 170 D then you work your way up through Research Xp points and £ currency.
The way you progress will be when you do missions, activities you earn Research point and Currency on completion and you must spend these to unlock extra attachments for that chainsaw increased bar length, increased HP performance, upgrade chains etc and then finally to unlock and purchase the next chainsaw in the sequence.
This way you must take the small jobs to start and with the more you progress the better equipment you can purchase to complete the bigger jobs given?
To much? You get my drift?.