There is no hard and fast answer to this question. It heavily depends on the size and geography of the planet, the technology level of the pioneers, the population of the pioneers and the resources available on the planet. Here is some explanation:
Size And Geography Of The Planet
Wrong levels of gravity are a bummer. We humans, are very fine tuned for life on Earth. And our solar system is exquisite (so far) in the sense that it contains very small planets. It is very likely that there are millions of rocky planets like ours, at the right distance from the parent star. However, since you have not established the size of your planet, I would treat it as an unknown variable.
For planets with lower or equal gravity to Earth (something between Mars and Earth), we can cope very well. For planets with higher gravity, we would face a host of problems. We would require larger muscles, thicker bones and larger lungs. This means the pioneers will be unable (or hardly able) to harvest any natural resources available on the planet and would have to subsist on supplies from home planet until evolution takes its course (or we genetically enhance our babies) and we have a sturdier generation which is able to easily survive and thrive on the planet.
So in case of gravitationally unfit planets, the investments will have to continue until suitable humans are produced. This might take as less as 25 years (if genetic enhancements are available) to as long as 50,000 years (for natural evolution).
As for the geography, a lot of investment will be required for a planet with no readily available water supply. For a planet where saltwater/seawater is readily available but there is no freshwater, major investments would be required for turning seawater into drinkable water (which would also be used for farming).
Technology Level Of The Pioneers
A higher technology level would require lesser shipments later on. By higher technology level I mean that the technological objects in usage are very dependable, durable, have high efficiency, can be run on solar energy and are miniature sized.
Obsolete and decommissioned pieces of technology require replacement, which translates to shipments (investment). Large sized technological objects (water filter plants etc) are easily damaged (in the long run) by sunlight, rain and other natural processes.
Population Of The Pioneers
This should be simple. A smaller number of people are not a good idea for populating a planet. The resultant population would be inbred and be very susceptible to epidemics. If initially a small number of pioneers are landed on a planet, later more missions would be required simply to provide more genetic diversity to the pioneer population.
Resources Available On The Planet
With an advanced metallurgy plant shipped with the pioneers and a high content of metals in the crust of the planet, it would be easy for the pioneers to create their desired metallic objects. Similarly, if a planet has life on it and earth-like trees, it would be very easy for the pioneers to harvest as much wood as required, to build extensive housing and other structures.
This again relates to the technological level of the pioneers. The higher technological level they have, the easier it would be for them to harvest the natural resources available to them.
In answering your question, I have assumed that you want the pioneers' generations to continue from the technological level of their parents. This is going to be a very hard thing. Without a proper society and all types of technological education and experimentation available to the next generation, they would not be able to grasp the scientific understanding of their parents, let alone build on that foundation.
Maybe the best idea is to send a group of pioneers on a very earth-like planet and let them start (technological) evolution all over again? Then send in enhancements once in a while (once every 30 years) to speed up the process. Build libraries, set up schools, colleges and universities, laboratories ... and have another, cleaner, purer earth with all the beauty of art and technology, but no problems of pollution, wars, violence and bad governance.