If your 928 is in Excellent condition, try selling it here or on Swappa for about $180 to $200 and then use that cash towards getting the Icon from Microsoft store or VZW. I do not know how your contract situation is so I cannot help you there. If you divulge a few more details perhaps others can chime in to help you out.
definitely try to sell the phone and put the proceeds toward the price of the Icon. VZW has an estimator on their site, they estimate giving you $54 for your phone here. totally not worth the trade in at all so selling prior would be best.
I did early edge when they had the offer, I don't know if they still do. Broke 928 screen sold phone on eBay then I had a RAZR HD for a few months then traded it in on early edge for lumia icon.