This is an intriguing question. The simple (but stupid) answer would be: the costs. Unfortunately high costs, on the one hand, are not an indicator for high rated research. Negative examples: "merchants of doubts" (Oreskes & Conway, 2010) are well paid, put the aim of their studies is clouding the public understanding and very often is low quality research. The amount of time one looses for accountability in EU sponsored projects does not increase quality. Inexpensive research, on the other hand, very often stems from independent researchers who benefit of academic freedom. Nevertheless cheapness cannot be considered as a quality criterion. What helps evaluating: looking at a researchers bibliography and wondering if there is a consistent research plan and a sense-making biography of a scholar behind it developing over a long period.  Research which implies heavy research infrastructures is obviously more expensive. Such infrastructures should be publicly financed. Very often governmentally ordered research, such as evaluation studies lack of means. The reason very often is simple: evaluation costs must be kept in proportion to programme costs. The consequence is that the questions asked cannot be answered properly. The research  fits the payment, and remains unsatisfactory. Very often a less ambitious evaluation, taking into account limits, can be more appropriate.  Though I have no clear cut answer and can only touch aspects of the problem, I think that behind your question stands really an essential problem of research policy. It is rooted in the fact that knowledge produced by research is not a commodity the quality of which would be proportional to its price and that research work must be considered as a regular mormally paid activity.

Good posts from both Charles and Heather,

Inexpensive - may not just relate to fiscal cost. It could relate to time and resources - and they are often determined by 'scale' and, I would argue, methodology. As stated previously though, it should never be about 'cheapest or easiest' - but far more about 'what is required to achieve what is needed'. For instance - a small-scale descriptive, exploratory qualitative study would usually be 'cheaper' than a larger-scale ethnographic study. A small scale, descriptive survey is more likely 'cheaper' than a larger-scale experimental trial.

Most of the inexpensive studies are observational studies

But when it comes to clinical trials it's usually expensive

Intelligent observations remains the most important for progress in science

it depends on the designs and the procedures of the studies. Usually, prospective studies required high fund to cover the expenses of the needed procedures, manpower and equipment. 

Thanks for all of you for your kindly explanations.

I am just concluding in little paragraph:

·         Inexpensive study would produce quality results and can be more useful in that it investigates vital questions.Heather

·         High costs are not an indicator for high rated research. Charles 

·         It should never be about 'cheapest or easiest' - but far more about 'what is required to achieve what is needed. Dean

·         Most of the inexpensive studies are observational studies. Mohamed

·         Prospective studies required high fund to cover the expenses of the needed procedures, manpower and equipment. Ahmad 

 It is clear that the research output value is the main indicator for the research rate assessment.