I'm trying to do exaclty the same - help would be appreciated

I did this by creating an XSLT Extension in my App_Code, with a method that I can call from XSLT:

[XsltExtension]
public class Business
{
    public Business() { } //required for the xslt extention

    public static decimal GetShippingCost(int shipmentMethodId)
    {
        Basket b = SiteContext.Current.OrderContext.GetBasket();
        OrderAddress shippingAddress = b.PurchaseOrder.OrderAddresses.ToList().Last();
        return GetShippingCost(shipmentMethodId, b.PurchaseOrder.OrderLines, shippingAddress);
    }
... 

    public static decimal GetShippingCost(int shipmentMethodId, ICollection<OrderLine> orderLines, OrderAddress orderAddress)
    {
        //logic to calculate shipping cost. Call this method from your custom shipping method, e.g.
        //decimal shippingPrice = Business.GetShippingCost(shipment.ShippingMethodId, shipment.OrderLines, shipment.ShipmentAddress);
        //return new Money(shippingPrice, shipment.OrderLines.First().PurchaseOrder.BillingCurrency);
    }

Then in your XSLT:

<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:msxml="urn:schemas-microsoft-com:xslt"
  xmlns:umbraco.library="urn:umbraco.library"
  xmlns:CommerceLibrary="urn:CommerceLibrary"
 xmlns:Business="urn:Business"
  exclude-result-prefixes="msxml umbraco.library CommerceLibrary">

  ...

  <xsl:template match="/">
    <form id="mainForm" method="post" action="...">
      <xsl:apply-templates select="CommerceLibrary:GetShippingMethods('Shipment')/shippingMethods/shippingMethod" />
      <input type="submit" value="Proceed to Payment" class="primary-action"></input>
    </form>
  </xsl:template>

  ...

  <xsl:template match="shippingMethod" >
    <input type="radio" name="shippingMethodInput" value="{@shippingMethodId}">
      <xsl:if test="@shippingMethodId = $shipment/@shippingMethodId">
        <xsl:attribute name="checked">checked</xsl:attribute>
      </xsl:if>
      <label for="{@shippingMethodId}">
        <xsl:variable name="shippingCost" select="Business:GetShippingCost(@shippingMethodId)"/>
        <xsl:value-of select="@displayName"/> - <xsl:value-of select="$shippingCost"/> 
      </label>
    </input>
  </xsl:template>
    

</xsl:stylesheet>

Hope that makes sense.

Zac

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