@Ritesh,
You can go for a cheaper natural gemstone alternative which I have mentioned below.
Instead of Blue Sapphire you can use Amethyst (comes in blue and violet color). For 5 to 6 carat it would cost around Rs. 400 to 500. Another option which will be little costlier would be Iolite (comes in blue and violet color) which might cost around Rs. 1000 to 1500 for 5 to 6 carat of a decent quality.
And, instead of Yellow Sapphire you can use Citrine (it comes in yellow color) and would also cost around Rs. 400 to 500 for a decent quality of 5 to 6 carat. Another option which will be little costlier than Citrine would be Yellow Topaz (comes in yellow color) which might cost around Rs. 500 to 1000 for a decent quality.
Read the simulants section at this page http://www.gemstonebuzz.com/sapphire which gives an idea which gemstones are similar to Yellow Sapphire and Blue Sapphire. Simulants in gemstone means the stone which appears similar in appearance to a particular stone.
More over, if you would like to buy these gemstones, you can go to ebay.in . If you need my help, let me know!