Formatage monetaire de nombre

Bonjour, je voudrais formater
les nombres de 3 champ dans un formulaire mais je n'y arrive pas.

Je voudrais un format de type : 1000,00 pour 1000
sur les variables du code ci-dessous :
var tt
var ttc
var vat

Merci pour votre aide

Code:

<script language=JavaScript> function Calcule() { var pr1 var pr2 var pr3 var pr4 var pr5 var pr6 var pr7 var pr8 var pr9 var pr10 var pr11 var pr12 var pr13 var pr14 var pr15 var tt var ttc var vat pr1=document.sponsor.company_logo_room.value*1200 pr2=document.sponsor.company_logo_website.value*600 pr3=document.sponsor.inserting_conference_bag.value*1200 pr4=document.sponsor.sponsor_badges.value*2500 pr5=document.sponsor.sponsor_computer_center.value*2500 pr6=document.sponsor.sponsor_welcome_reception.value*2000 pr7=document.sponsor.sponsor_exhibitor_cocktail.value*2000 pr8=document.sponsor.sponsor_coffee.value*2500 pr9=document.sponsor.sponsor_social_evening.value*2000 pr10=document.sponsor.back_cover_page_final_program.value*1500 pr11=document.sponsor.back_cover_page_abstract_book.value*1500 pr12=document.sponsor.first_cover_final_program.value*1200 pr13=document.sponsor.first_cover_abstract_book.value*1200 pr14=document.sponsor.pack_3.value*1150 pr15=document.sponsor.industrial_presentation.value*2500 tt=pr1+pr2+pr3+pr4+pr5+pr6+pr7+pr8+pr9+pr10+pr11+pr12+pr13+pr14+pr15 vat=tt*0.196 ttc=vat+tt document.sponsor.ht.value=tt document.sponsor.vat.value=vat document.sponsor.ttc.value=ttc } </script>