The five gemstones in the wedding band could mean many different things to different people, but the popular symbolism is the number of years they spent as a happily married couple. To make it even more special, you can go for a five-diamond ring with an open gallery featuring a diamonds cluster floral design that is encircled by diamonds halo.
You could very well go for five round brilliant cut diamonds that match one another, with each one weighing at least around 0.20 carat. That adds up to about one carat, so the cost of the diamond ring will be well within your budget, of course. When on it, choose a white precious metal to complement the overall aesthetic appeal of the five-diamond ring. If you do not want platinum, you can go for 14k white gold instead.
Note that although white gold is a durable metal, it may cause allergies on those who are prone to that. That aside, it looks every bit gorgeous as platinum but costing much less in comparison. Additionally, it is generally advised to choose F to G color grade, and VS2 clarity grade, for smaller diamond accents. This way, the diamond ring would not cost you an arm and a leg.