How do get value of razor textbox in the same view?

I am using `@Html.Textbox("searchString") in Razor view page. I need this value of textbox in

@Html.ActionLink("View Items", "Index", new { id = item.transaction_id, searchString = "Value of textbox"}).

Of course the search string part in html action link is not working right now but i need this as i have specific route which works according to search string.

How do i pass value of textbox to action link?

i check this this,this,this and this.

What i tried is

<script type = "text/javascript">
var value = document.getElementbyID("searchString").Text;
var link =  @Html.ActionLink("View Items", "Index", new { id = item.transaction_id, searchString = -1});
link.replace(-1,value);
</script>

Still no luck. I understand Razor renders at server side.

UPDATE

i have following textbox on the top of view:

    @using (Html.BeginForm("Index", "trans_junction", FormMethod.Get))
{
<p>
    Request No: @Html.TextBox("searchString")
    <span><input type="submit" value="Search Request" /></span>
</p>
}

This textbox is search box in which user can search items.

there is an Action link as follows:

 @Html.ActionLink("View Items", "Index", new { id = item.transaction_id }) |

and a route config:

public class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}/{searchString}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional, searchString= UrlParameter.Optional }
        );
    }
}

Now i need to pass the values as my route map via actionlink. As suggested in answer by StephenMuecke, i tried to modify my @using (Html.BeginForm("Index", "trans_junction", FormMethod.Get)) with @using (Html.BeginForm("Index", "trans_junction", new { id = item.transaction_id }, FormMethod.Get)) but item is not accessible there.

When user click search button, url is http://localhost:57286/trans_junction/Index?searchString=20

if user click on Action link url is http://localhost:57286/trans_junction/Index/88

but i actually need is http://localhost:57286/trans_junction/Index/88/20

which preserve the the result of search and also pass the id.

I am adding screenshots for better understanding.

This is index view without search.

This is search result with searchString = 10.

This is after clicking the action link i.e. View Items, Here search results are not preserved.