This was speculated on before, the price. In Japan, like stated, the usual price for a DS game would be 4800 Yen. So, with the bundles in PokéWalk device, it should only go up a few more around 5000 Yen, if any. This is a special package, so prices shouldn't be lifted to any higher price, because then it would be basically like buying two things for the extra cost. Not to mention, when you include the cost of shipping, the price would go up for the buyer of couse. However, in the USA, the regular price for a DS game is about $35.00 and that is for the game alone. Usually, when things are included it would go up to about $40.00 - $50.00. So, things shouldn't be raised to an upright high price. In addition, the PokéWalker isn't currently known to hit outside of Japan, and if it isn't, then the US price for HeartGold and SoulSilver will remain at $35.00 for the most. As for the Japanese price converted to US Dollars, it should be just about $52.05, but this does not include the cost of shipping. So, My guess would be a roughly in the early to mid sixties, depending where and from who you purchase the game from.
Note: When countering the prices, tax and shipping were not included, but mentioned.