Gas prices are up throughout the country, and in Waltham prices have reached a high of $4.09 per gallon. Ouch. Waltham Patch is all about keeping you informed, and we'd love to help you save an extra dollar or two when possible. With that in mind, we've compiled a list of the cheapest gas in Waltham. We created the list using the MapQuest cheap gas tool, which was built by our parent company, AOL.    Three cheapest gas station in Waltham (all prices for regular unleaded and prices are subject to change). High Street Express, 196 High St., Waltham: $3.69 Hussem Jacob, 1232 Washington St., …