Visa for Russia

http://www.visatorussia.com : 50USD for invitation + fake trip plan
http://www.homevisas.com/Dossier/russie.html : 75€ for invitation + fake trip plan
http://studyrussian.com/MGU/visa_application.html: 70USD for invitation + fake trip plan
http://www.gotorussia.net/visasupport/russian_visa_support.htm: 29USD for invitation and i'm not sure what else
http://www.realrussia.co.uk/visa/tourist_visas2.asp : £75 VISA included ?
http://www.waytorussia.net/Travel/VisaSupport.html : 30USD for invitation valid for 30 days stay
... i even had a guy on the phone who was ready to sell me the invitation only for 190€!! (and the VISA for 220€ on top of that!)

There are so many of these agencies out there and the prices are so different it gets really confusing..
Has anyone out there already -successfully or not so successfully- used any of these services? you may even make the list longer if you whish.. but please share valuable experience.. Am i cool with a 30 bucks invitation? if not, why?

Thanks people!