I'm not very keen on the balloon idea, the reason is it always seem to entice the children at any wedding to go 'hypo'... running around, with these balloons, running into people with drinks and food, and 'wafting balloons' all over the place, not to mention when 'they pop' them on purpose !

I like the idea of those 'small cameras' you can supply for your guests... this way they can take their own photos seated at the table, and at the end of the night, you can collect them... this way, you have more fun, and memories, looking back at what they were up to on the night..(and can be placed in your 'guest book') or shared.
You can buy them on the Internet, quite cheaply, and in different colours, and can be placed in a bowl in the centre of each table.

If you do still want balloons, the cheaper option, to fill the vase up, is I would suggest, silk flower petals, or real petals, in the colours of your wedding outfits.

a friend x