you don't need a massive one for the 350D, i use to get by on a 2gb for my old old 300D...
thing is nowdays its impossible to get anything below 4gigs haha so you might actually want to have a look at like courts or harvey norman that kind of deal and see if they have some older, smaller cards..
speed isnt really important i wouldnt say since you shooting at most what like 3fps? and i don't reckon the 350D is umda compliant anyway... so like 133x maybe even 300x if you can find should be fine..