Small rockets have the potential to play an important role in the changes that are now occurring in the spaceflight domain. Currently, satellite miniaturization is opening up new possibilities to form constellations capable of full-time global coverage for internet service, real-time earth observation applications, and disaster monitoring. Such programs involving small satellites require low-cost and frequent access to orbit. A new class of launch vehicles is uniquely positioned to offer these small satellites dedicated access to space, with no restrictions on target orbit height or inclination traditionally associated with current rideshare arrangements. A number of new launch service providers has stepped up to this challenge, developing systems with decreased size and payload capability in a commercial way. Their offerings are priced lower than costs traditionally associated with a rocket launch. However, most of these firms do not have hardware in production yet, so the question arises whether or not these early price quotes are realistic with respect to the actual costs incurred. This research has made a first step towards answering this question, by developing a way to estimate costs for such systems in partnership with the European Space Agency’s Cost Engineering Section. All aspects of the estimating process were addressed, from gathering and selecting data, to building Cost Estimating Relationships, detailing cost-risks, and employing existing - and developing new - parametric relationships, whilst exploring their applicability to systems that have a lower payload capacity and gross lift-off weight than traditionally larger rockets. An early phase parametric cost estimate was synthesized with which it is now possible to approximate for commercial liquid and solid propellant rockets in the 100-700 kg payload range the development, production and operating costs, and their cost-based price per flight to within 20% of reported costs. By doing so at an equipment-level depth, novel contributions to theory could be made by adapting the Theoretical First Unit T1method of estimating,mirroring the reductions in cost achieved by commercial launch operators through profit retention and reduced subcontractor management effort. Whilst exploring these new launch vehicles’ costs, it was also discovered that small rockets in particular require a launch rate of over 4 per year to keep program commercialization expenses fromcausing up to a threefold increase in launch prices. An ESA liquid methane vehicle concept was central to the estimate; it was however concluded that this rocket ineffectively addresses the LEO market at a price point that is too high to gainmarket share. Nonetheless, other future proposals for small launch systems can now be evaluated for their cost feasibility, either by potential investors or agencies seeking shared technology development with commercial partners.