It depends on the type of library to be prepared. Before starting the library preparation, we perform a quality control on each RNA sample. Typical amounts of total RNA for mRNA-Seq libraries are at least 5 µg of high quality total RNA per sample.
In addition Eurofins Genomics does offer you cDNA library protocols for samples with really small amounts of starting material are available, like clinical samples, sorted cells and others. If you need a service partner for such projects just contact us.