dude you would definitely scope out craigslist or even gamestop for a used 'network adapter' (NA) instead of spending extra cash on a slim. let ebay be your last shopping place to resort for buying a NA. i once saw a used NA at gamestop for $15!
the NA will allow you to plug in an 3.5 in. IDE hdd (get maxtor or seagate barracuda) to the PS2 bay (back of the console).
PS1/SCPH-7501 | MM3 modchip
PS2 v9 | 250GB hdd | PS3 component cable | katana 32mb mc
PS3/CECH-2001B | 250GB hdd | 3.65 ofw