"...price cap to what you can import..." More about exporting firearm parts on the U.S. restricted for export list. The U.S. has recently decided we aren't selling firearms etc to terrorists so they upped the max value that can be exported. However, if the box/paperwork says M-14 on it, it's illegal to export without the U.S. Dept of State permit. The manufacturer must have a U.S. Commerce Dept exporter's licence for any part too. So if you mention M-14, it'll be stopped at the border by U.S. Homeland Security. If the box/paperwork says M1A on it, everything is fine.
None of this will get you in any kind of trouble though. Just the seller. You just won't get the parts and will very likely lose your money.
Both Brownell's and Treeline should tell you upon ordering if they can export the part. Your order isn't worth losing their business over.