I have a tri-top from underworks that I bought used from somebody.  It's stretched out at the top and bottom so it sticks out and can be seen easily through my shirts.  Layering doesn't work well because all my shirts are so big they bunch up and look weird if I wear more than one. 

I wondered if anybody knew of a cheap lycra undershirt or something similar that I could get?  Just a light, tight shirt made of slick fabric like a binder, to hold the edges down?  I've seen stuff in the sports section but it's usually pretty expensive. 

I dont know if this helps, but i have an underarmour shirt like how you're describing. I have one from the company underarmour that was like 25 dollars. I have one thats like identical from walmart that was only 7 dollars. It works for me.

Wow, really?  Yeah, I'm looking for something like Underarmour, but I've never found anything at Walmart that wasn't around $20-30 before.  Maybe I'm just looking in the wrong place?

I dont know, maybe it could just be diffrerent where we live? I bought mine months ago but i was at walmart tonight and they still had them.

http://www.walmart.com/cp/All-Activewear/592999

the short sleeve compression t is the one i have. 10 bucks on the website. Works really well though, just as good as the underarmour at least.

I buy compression shirts --- I wear them every day with my binder --- I am so sick of those tumors!

I get my compression shirts at walmart, target, Kohls, T.J. max  --- I make sure they say compression on them otherwise they don't work nearly as well -- all of mine have been under $20

Thanks guys!  And thanks for that link, Michael!  If I can't find one in the store I'll probably buy one from there.

I just checked the sizes, and a small is 34-36" across the chest...  I need something closer to 28" or it will just hang loose on me.  I've tried looking in the boys' section but haven't had much luck..  Anyone know where you can get extra small clothes? 

http://www.kohls.com/kohlsStore/kids/boys820/athleticapparel/tops/PRD~637675/Tek+Gear+Compression+Tee.jsp

This is the youth department ... Compression shirts are designed to fit snuggly ... I know bike stores also carry lycra shirts

Qut of curiosity I looked and wondered why I never saw one like this in walmart. According to this site the stores around me don't carry them.  Go figure.

I looked there, Rob, but the sizing chart didn't list boys' sizes?  And the young men's measurements were actually larger than the men's.  Where I used to live the stores didn't carry them, but since I've moved the internet says they do, so I guess I'll just have to do some looking around.

Farm boy, looks like you'd need a boys medium probably. Click the size chart link, then at the top of the page there are tabs, click the one that says kids, then boys 8-20 tops. According to that, a boys M (10-12) is 28-29 inches in the chest. Hope this helped

Oh gosh, now I feel dumb.  Thanks Konnor!