One of the cheapest seedbox provider which is equally reliable is CUtorrents , CU Torrents have been in business for quite some time and right now they are expanding their business, if yo are really planning to increase your ratio in private trackers 500 GB hdd is a definite requirement with small HDD space your chances of making a decent ratio in these private trackers is pretty slim .
Here you can see that for 14 $ a month you are getting 500 GB hdd unmetered traffic 100 mbps line , I think this is the best deal around.also they have SSl access and file transfers through FTP, so transferring files and uploading files into the servers is equally easy.
Now compare it with the cheap seed-boxes which are like 3-4 $ bust the amount of space they provide is so negligible that it will take you eons to make a decent ratio also mostly they have capped bandwidth and unless you are planning to use a seedbox only to have fun its pretty pointless getting a seedbox with a 5-20 gb hdd.