Yes, replace this line:
retstr += Field ("issue_date"+i)+"<t><t>"+Field("check_number"+i)+"<t><t>"+Field("check_amount"+i)+"<br>"
with this:
retstr += Field ("issue_date"+i)+"<t><t>"+Field("check_number"+i)+"<t><t>"+FormatNumber("$###,###.00", Field("check_amount"+i))+"<br>";
That will put in leading dollar signs, commas at the thousands place and force two zeros after the decimal.