It would be for a very simple/basic gown and suit, likely not from a bridal shop (think those generally will cost more due to higher rental/overheads/markup). Cheaper options will probably be from like smaller businesses.
Think a gown can be 3-600++ alone (depending where you rent from and the complexity/quality you choose), suits should be around the same range. A general budget might be $5-600 for rental of both. On the low low budget end $3-$400 might be possible, as there are options, although the dress/suit options will probably be more limited. E.g., The link I shared previously has simple dresses from $68-$188. Cheaper suit rental I saw at $100+ range from this place via google search: http://www.mysingaporetailor.com/rental_choose.php Never used them though, YMMV. Put together that would be $300+ roughly.
For 1 x gown rental only our vendors charge 350 for 1 gown, but of course if you want to get 1 gown or 2 gowns + suits it will be cheaper when you divide per piece. around 688 for 2 gowns/838 for 2 gowns + 1 kua/suit.
for suit i will recommend customizing a bespoke suit. our vendor charge 350 for 2 piece suit!