Having just visited many stores on the search for the perfect-fitted, affordable OTR shirt, I made the following ranking based on how slim the shirts are, in general (not taking specific measurements, etc.). For reference, I'm 5'8'', 145lb, ~10% BF (14'' neck, 33'' sleeve, 36-37'' chest, 29'' waist). The price ranges are what I expect to buy for, when they're on really good sale. Also, please be aware that everything is biased, based on my own experiences.
13. Lands End - S (Tailored Fit) [$15-30]: An entire size too big. Good quality for the price.
12. J. Crew - S [$30-45]: Pretty boxy; practically an entire size too big. Great quality.
11. Banana Republic - S (Regular) [$30-40]: Pretty boxy. Quality is a step lower than J. Crew's.
10. Express - S (Fitted) [$35-45]: Typical "slim-fit", but still too boxy for me. Horrible quality.
9. Old Navy - S (Slim) [$15-20]: Slightly slimmer than Express'. Horrible quality, but it's expected.
8. Club Monaco - S (Slim) [$30-40]: About the same as Old Navy's. Quality is a step lower than J. Crew.
7. J. Crew - XS [$30-45]: Slightly slimmer than Old Navy's, but still not slim enough for me. Great quality.
6. Banana Republic - S (Slim Fit) [$30-40]: Slightly slimmer than J. Crew's. Quality is a step lower than J. Crew's.
5. Brooks Brothers - S (Extra-Slim Fit) [$40-60]: Slightly slimmer than Banana Republic's; great fit. Amazing quality.
4. H&M - S (Slim) [$15-25]: Slightly slimmer than Brooks Brother's; ideal fit. Poor quality, but suitable to the cheap price.
3. Zara - S (Slim) [$40-50]: About the same as H&M; ideal fit. Pretty poor quality.
2. Express - S (Extra-Slim) [$35-45]: Slightly slimmer than Zara; a little too slim for my tastes. Horrible quality.
1. Club Monaco - XS (Slim) [$30-40]: Slightly slimmer or same as Express'; a little too slim for my tastes and collar is just a little too small. Quality is a step lower than J. Crew's.
Notes: I forgot to write down whether the J. Crew shirts I tried on were Regular or Slim-Fit (I think they were Slim, but I'm not entirely certain). I should also try on Banana Republic's XS Slim just to see how it compares to Club Monaco's XS Slim.
In conclusion, BB ESF and H&M Slim are my two favorites. H&M has my preferred fit, but the quality is nothing compared to BB's. In contrast, BB has amazing quality, but it's slightly too boxy compared to H&M's fit. However, this small difference in fit is pretty negligible compared to the huge difference in quality. Thus, I use BB for my main versatile shirts, whereas I have H&M shirts for back-ups, less-popular patterns, more extravagant colors, etc. Wardrobe-wise, I plan to keep ~5 BB ESF shirts and ~5-7 H&M shirts (if I weren't a poor grad student, I'd use BB or MTM almost exclusively). Banana Republic might be a good compromise between H&M's prices and BB's quality, though I know how much SF abhors its quality.
You're getting great prices... I see J. Crew shirts selling at 70.