It might be helpful to say which MSP430 part you're looking at. I use the G2 Launchpad to flash the MSP430G2xxx parts using 2-wire JTAG. That works with the chip installed on the Launchpad, or in-circuit with jumpers. But I don't know if that Launchpad would work with your part.
But the least expensive option for one-time use might be to flash using BSL. You would use either BSLDEMO or BSL-Scripter software, depending on how old your part is, and a jellybean USB-to-UART adapter module like the CP2102, FT232, or CH340 as the interface. TI doesn't support those interfaces, so you would need some software mods and instructions, which are available from me. Of course that assumes your chip has BSL. Not all of the early ones do, but slau319t.pdf would tell you if yours does, and if so, what software it requires.