It is important to recognize that there are large differences in the quality of service that editors provide. Since research funding is often scarce, it can be tempting to go with an editor who will only charge 60-80 euros for a 20+ page manuscript. However, the editing will probably be light and focus exclusively on glaring errors, such as incorrect verb tenses, obvious idiom problems, and spelling mistakes. This type of editing will clean up the manuscript to a certain extent. However, it will do nothing to deal with the types of issues that most often provoke reviewers to ask for English editing: those pertaining to sentence structure and fluidity.
For example, take the following sentence, which came to us in an "edited" manuscript:
“Because of their abundance in most terrestrial habitats, their foraging decisions may have important consequences at the ecosystem level.”
At first glance, it seems correct - there are no problems with subject/verb agreement, incorrect verb tenses, or improper preposition use. However, if you look more closely, the sentence is actually rather confusing. It appears to be saying that “their foraging decisions” - the grammatical subject of the sentence - are abundant in the environment and thus have important consequences for ecosystems, which makes no sense.
Now consider our alternative:
“Because ants are abundant in most terrestrial habitats, their foraging decisions may have important consequences at the ecosystem level.”
A small but important change suddenly makes the meaning clear – the ants are the ones that are abundant, and it is their foraging decisions that are of consequence. These types of more complicated, yet crucial, grammatical issues often get ignored by those doing quick, cheap editing. In fact, we have recently spent a lot of time on this blog discussing similar issues (see our series on "Reader Expectations") because addressing this kind of problem is extremely important, but often overlooked, in helping readers (and reviewers!) follow your thoughts.
As a consequence, while we may charge as little as 60 euros if the editing is light and the manuscript short, we will not accept a job only to do it halfway; some manuscripts clearly need more thorough editing. It is for this reason that we offer price estimates only after having looked at a text. Additionally, if a manuscript has already been submitted, we like to look at reviewers’ comments to see examples of the types of corrections they are requesting. Knowing exactly what kinds of problems need to be addressed helps us, and ultimately our authors, to improve the language of the text as much as possible. It's self-serving for us to say so, but it really is true: investing a little more in your editing budget upfront will help you save time and money in the long run!