[SalesForce] How to make field conditionally read-only without Javascript

A wrapper class is useful in this scenario. There is not enough controller code in the question to know for sure, but the implementation may look like something like this:

In the controller, define the wrapper class and change the method to return wrappers rather than sObjects. The controller will build the wrapper and set the isRendered member variable based on whether the sObject is contained in a Set someplace else in the controller.

public class ProposalWrapper {
    public Proposal__c proposal     { get; set; }
    public Boolean     isRendered   { get; set; }
}

public List<ProposalWrapper> getProposalWrappers() {
    List<ProposalWrapper> proposalWrappersToReturn = new List<ProposalWrapper>();

        // iterate over the list of Proposal__c sObjects
    for (Proposal__c proposal : ProposalsFromSomeList) {

        // create a wrapper to allow you to indicate visibility
        ProposalWrapper pWrapper = new ProposalWrapper();

        // stick the sObject into the wrapper
        pWrapper.proposal = proposal;

        // set the boolean field true/false based on whether the item is in the set
        pWrapper.isRendered = yourSet.contains(proposal);

        // add the wrapper to the list being returned
        proposalWrappersToReturn.add(pWrapper);
    }

    return proposalWrappersToReturn;

}

In the page:

<!-- iterate over the wrappers and use the boolean field to control visibility -->
<apex:repeat value="{!ProposalWrappers}" var="item">
    <apex:outputPanel rendered="{!item.isRendered}">
        <li>
            <apex:outputText value="{!item.proposal.Id}" />
            <apex:outputText value="{!item.proposal.Name}" />
    </apex:outputPanel>
</apex:repeat>

One way you could make this work is HTML5-ifying your Visualforce page and use <apex:input type="number" /> instead of apex:inputText.

Otherwise, you could implement some javascript validation or send it back to your controller and do the validation in Apex.

Note: To HTML5-ify your page, the easiest way is using the page element with the docType attribute <apex:page docType="html-5.0">.

See: http://blogs.developerforce.com/developer-relations/2011/12/visualforce-html5-mobile.html