You can still use quotes.
I'm not sure how familiar you are with Business Process Flows in CRM. But your process would look something like this:
Lead/Customer > Opportunity (Create Opportunity Products) > Quote (Get Opportunity Products) > Opportunity (Convert to Work Order) > Work Order > Invoice
So you will qualify a lead or existing customer to an opportunity. Then you will add potential Opportunity Products that your customer is interested in. Once you are happy you can create a Quote which will pull in the Opportunity Products from the Opportunity (Using the Get Products functionality) and then you can possibly send out a report of the quote to the customer or how ever you give out that information. Once the customer is happy with the quote you will return to the Opportunity again to convert the Opportunity to a Work Order which then eventually will generate an Invoice once the work is complete.
Your Process sounds quite simple. Which is a good thing.
Your Field Techs can create a parts request and you will receive them in the back office via CRM. Then you will order those parts to your current location and receipt them yourself, then you can distribute them to the Field Techs.
