I believe this functionality does exist, to some extent, within the Supplier Tendering.
I have not used it myself, so I recommend you read this section of the manual: http://www.weberp.org/weberp/ManualConte...ierTenders
Andy is right, I wrote the tendering system to be flexible so you can either send tenders to suppliers asking them to submit quotations directly on to the system, or the supplier can be set up to just submit what are called "offers", effectively quotations without a tender so should be flexible enough to meet your requirements.