If you are not happy with the price on a proposal you have a number of options:
You can use the Comments Channel to let a firm know that you would like a revised price. The firm can then submit a revised total price and you can see both prices in the Comparator table. They can keep revising as often as you need until the Proposals Due By date has expired or an auction has ended. If that happens and you still wish to receive revised proposals, you can re-open the Request.
You can invite other firms to submit proposals and compare the original proposal with competitor proposals.
You can choose to invite firms to a Reverse Auction via a new Request (you can do this by copying the original Request and enabling the reverse auction feature before you send it to firms).