If your buying in the USA I would look at offers from gymcor.com, I have had clients that have purchased some great machines at great prices and speak very highly of the service they have recieved.

If your located in Europe I would start with www.healthclubsathome.com, who also have a good selection of treadmill, cross trainers, bikes etc and are located in the UK but deliver

throughout Europe, yet again lots of good feed back from previous clients.

GOOGLE BLOGSPOT http://secondhandgymequipment.blogspot.com/

Need a complete gym set up http://www.gymkituk.com