I believe the price in Penang which are way overrated compare to Kuala Lumpur is mainly because the place that you been visiting is a tourist trap. I'll give you some price comparison of Penang food price (good food) vs KL (average) on same food that you interest to eat.
1. wan tan mee (standard price in penang around RM3-3.50)/ KL at least RM4.
2. Cendol (Penang famous cendol at Penang road is around RM2-2.50/bowl), KL at least RM3 and above
3. Laksa (RM4 for the good one), KL I believe is the same price or at least RM5 (with fake label claim as Penang Laks)
4. Durian (debateable price as sometimes it is more expensive compare to KL). Depends of the varieties and origin of the fruits
5. Hokkien mee (RM3-4. some famous one charge as high as RM5-6). KL standard price is around Rm5
6. Char koay Teow (Penang: overprice. Some as high as RM10). Honestly, the normal stall which charge around RM4 is good enough)
7. Seafood. way more cheaper than KL
8. Thai food. Way more cheaper than KL
9. Indian vegetarian food. Way more cheaper than KL
10. Nasi Kandar. Getting more and more expensive. Around RM20++ and tourist usually get con and overcharge (um... local also the same). Any Yes. Nasi kandar, tandori chicken, roti naan are all expensive food which surprisingly generate good business. You can have a great western buffer lunch/dinner at your hotel at much cheaper price if you chose to go for full fedge course on Nasi kandar food.
11. Taxi. Everywhere is expensive and mostly don't use meter
12. Local Fruits tend to be cheaper if you visit the morning market
13. Sate Most expensive in Penang will be RM1/stick and cheapest one will be around RM0.50 at night market. Whereas the most famous satay in KL (Satay Kajang will cost around Rm0.8/stick) whereas the city will still charge around RM1++/stick)
Apart of the pricing and advantage of Penang pricing compare to KL. Do take note that there's a few thing regarding food in KL which is better than Penang.
1. KL food Portion are usually more compare to Penang even though if you encounter less desire noodle.
2. Dim sum in Kl is still the best compare to Penang. But if you taste Hong Kong Dim Sum, I don't think Penang/KL can beat them
3. More variety of food/restaurant/choice avaiable in KL compare to Penang
4. Although KL food , I believe is more expensive. Those charge higher price usually have better hygeine whereas the famous and cheap hawker food recommended above tend to be a bit dirty. It won't upset your stomach but well,...maybe your eyes won't be happy about it.
Edited: 4:45 am, November 06, 2013