For example:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
      version="1.0">
<xsl:output method="xml" omit-xml-declaration="yes"/>
<xsl:key name="comp" match="item" use="name" />
<xsl:template match="/">
<table border="1">
	<xsl:apply-templates/>
</table>
</xsl:template>
<xsl:template match="item">
	<tr><td><xsl:value-of select="name" /> </td>
	<td><xsl:value-of select="price" /></td>
	<xsl:for-each select="component">
		<td><xsl:value-of select="cname" /></td>
		<td><xsl:value-of select="quantity" /></td>
		<xsl:variable name="cn" select="cname" />
		<xsl:variable name="q" select="quantity" />

	<xsl:for-each select="key('comp', $cn)">
		<xsl:variable name="p" select="price*$q" />
			<td><xsl:value-of select="$p"/></td>

---------------------------
Test (must be within scope of the $p variable):

<xsl:call-template name="loop">
      <xsl:with-param name="pr" select="$p"/>
</xsl:call-template>
---------------------------

	</xsl:for-each>

		<!-- <xsl:value-of select="quantity" /> -->
	</xsl:for-each>
</tr>

</xsl:template>

<xsl:template name="loop">
	<xsl:param name="pr"/>
	<xsl:param name="t" select="0"/>
	<xsl:message>pr=<xsl:value-of select="$pr"/>, t=<xsl:value-of 
select="$t"/></xsl:message>
	<xsl:choose>
		<xsl:when test="$pr">
			<xsl:call-template name="loop">
			<xsl:with-param name="t" select="$pr+$t"/>
			<!-- I presume you meant to add: -->
			<xsl:with-param name="pr" select="$pr -1"/>
			</xsl:call-template>
		</xsl:when>
		 <xsl:otherwise>
			<xsl:value-of select="$t" />
		</xsl:otherwise>
	</xsl:choose>

</xsl:template>
</xsl:stylesheet>

-- 
() ASCII Ribbon Campaign  | Joe Kesselman
/\ Stamp out HTML e-mail! | System architexture and kinetic poetry