design problem.

you have:

customers
vendors
bids
parts
request for bids
orders


Just think about your relationships again here.
Think like you might think with ActiveRecord associations. (in fact  
that's probably what you need here)
You're trying to do too much with one model. (that's more like C  
structs)
You need more models that can interact with each other. (more like  
Ruby objects)
You may need to break it down further...

But just make your little sketches on paper.
There are a few perspectives you could take here, but start with the  
most basic items
You may need to alter the naming. Sometimes it can be confusing.
is a bid the price offered by a vendor?
or is a bid the whole response from the vendor?

One thing to be wary of are words that are verbs and nouns.
objects tend to be nouns and methods tend to be verbs or predicates.