American Apparel makes the best T-Shirts in my opinion; best for people in relative good shape as they are not loose in the trunk, and the fabric is higher quality and a bit thicker so they'll last a long time.
http://store.americanapparel.net/men...-t-shirts.html
Stafford is also a good brand that's significantly cheaper in price, but only marginally lower in quality. Going to a Penny's you'll see 2 for 1 sales often.
http://www.bizrate.com/mens-tshirts/stafford-tshirts/
Buy dress shirts between seasons as the department stores are trying to clear the inventory for incoming apparel. You can often find 50-75 percent off at these times. So sometime between now and the end of september a place like Dillards will have such a sale. Murano makes a great quality shirt for cheap, and they fit very well for an average build.
Dillards Link
I'd recommend checking out Moderntailor.com to buy 2 or 3 made to measure shirts. They have some great quality shirts available, but make sure you're generous with your measurements. I've found that they cut the cloth on the conservative side of things. So if you are a 32 waist, order a 33. Or if your arms are 25 in length, get 26.
If you have more money to spend, go to jhilburn.com and see if they can send out somebody to measure you and bring samples. They are much more expensive than moderntailor but the quality is top-notch and service is impeccable. I bought a pair of pants, but they didn't have a demo to show me so when I told them I liked the pants but they were just a bit thicker than I was expecting, they gave me a free pair of pants of my choice and let me keep the original order.