Have you actually read my
posting on this thread? Data roaming is prohibitively expensive within Europe and given your colleague's requirements absolutely infeasible. The linked Wiki lacks the probably best choice for your requirements, Lidl. With a Lidl SIM that costs € 9.95 and includes € 10 of credit you could subscribe to the dayflat tariff which would give you 500MB per 24h for € 1.99/24h. In contrast to other German prepaid providers you really get 24h while others bill by calendar day, so whenever you start a data session it ends at midnight.