when assiging resources i saw only work, material cost but i didnt see equipment. how can i assign the cost of excavator equipment for example? which type should i use?

You have a couple of choices:
You can create the excavator as a work resource, specify the cost per hour on the resource sheet and assign the excavator like a human resource. The work for the excavator will be added to the work for the task.
Downside: it is impossible in project to tie the excavator and excavator operator together and you may end up with the operator working without the excavator and the excavator working without the operator.
If you need to account for the cost of the excavator and also need to make sure your operator and equipment work together, create a resource that stands for both resources together -- for example: Excavator 1 and Bob. Increase the cost for the resource to include both Bob's cost as well as the equipment cost.

If you just need to track costs, and are not concerned about tracking availability, create the cost resource and assign the cost resource to the task.

I hope this helps.

Julie

by impossible to tie you mean, you can not tie two resources together in ms project right?

Yes, you cannot force two resources to work together on a single assignment. Each resource is scheduled on the task based upon his/her calendar.