:salamext:
A reasonable mahr is simply one that is reasonably affordable for the groom, i.e. one that will not burden him, or put him in to debt.
I remember reading the book of marriage, particularly the chapter on mahr, in al-Mulakhkhas al-fiqhi, by shaykh Fawzaan helped me a lot when I had to make such a decision. I remember this quote by Ibn Taymiyyah in that chapter:
"If the dowry given is much, it is not deemed detestable as long as the groom is able to afford it, unless the large amount is offered for detestable purposes, such as boastfulness, showing off, and the like. However, if the groom is unable to afford such a large dowry, it is detestable for him to present it.
[...]
If the amount of dowry is much and it is deferred to be paid later, it should be deemed detestable also due to the difficulty caused to the groom by the burden."
An interesting point that the shaykh expalined, was that whatever the girl's father/guardian requests from the groom, such as clothes or jewellery, this counts as the mahr. So yes sisters, be reasonable in this matter too. I know in the Somali culture, the groom has to present the wife with suitcases full of duroo3 (a type of dress, typically worn by Somali women), which are normally bought from the Emirates nowadays, and loads of gold, as well as the mahr. Obviously, that puts a lot of strain and burden on young brothers who are struggling to get married.
Shaykh 'Uthaymeen (rahimahullaah) stated:
"Extravagance in dowry payments and wedding celebrations are all in conflict with the Islamic Law, because the most blessed marriage is the least expensive one; and the more the expenses are decreased, the more the blessing are increased."
- Fatawa Islamiyah - ;The book of Marriage; Volume 5, pg.300
And as for all those sisters who are whining about making hijrah, or going abroad to study the deen. If you're really sincere, then you won't place your husband in to endless debt, for this dunya, or status etc. I say status, because a lot of the time it's all social status, and israaf. Really, do you think any amount of money can cover what you're worth? The mahr is a gift, not a price tag.
I'll just end with the speech of our Messenger (salAllaahu 'alayhi wa 'ala aalihi wa sallam) on this matter:
Uqbar bin Amir (radiyAllaahu 'anhu) narrated that the Messenger of Allaah (salAllaahu alayhi wa sallam) said, "The best dower is the easiest one." {Related by Aboo Dawood. Al Haakim graded it as saheeh}