Honestly if you have little money you should invest in demystifying bike mechanics. Spend your money on tools, not fancy parts. A rack can be had for cheap, and a properly installed P clamp can be as reliable as braze ons.
Nothing will kill a long tour faster than having something grinding on you that you don't know how to take apart and replace. If you know how to do that it is just an inconvenience, not an expensive reroute to a bike shop.
Get the oldest bike you can find, if it is rusted even better. Chances are it will be free. Chances are you'll have to fight the bike for every part you have to take out which would be great; the experience will teach you more than years of reading about it.
As we speak I'm literally dissolving an aluminum seatpost on a steel frame with sodium hydroxide (lye) because it was stuck beyond human power to remove. That is a bit extreme but the point is, you learn by doing. The first time you break a bolt on a braze on (ideally on the beater free bike you use to learn) you will pick up a ton of knowledge that will keep you safe and rolling in the wide road.