I see, I left some code I should have removed. I think it should be:
<input name="amount" type="text" id="amount" value="<%=FormatNumber((WA_eCart_GrandTotal(WA_eCart1) * .3),,,,0)%>" />
If that doesn't work, what if you just used:
<input name="amount" type="text" id="amount" value="<%= Round((WA_eCart_GrandTotal(WA_eCart1) * .3),2) %>" />