Shaykh Muhammad ibn Saalih al-'Uthaymeen (may Allaah mercy on him) was asked a similar question and said:

The ruling on that is that it is contrary to the command of the Prophet (Peace And Blessings Of Allaah Be Upon Him). The Prophet (Peace And Blessings Of Allaah Be Upon Him) said: "If there comes to you one with whose religious commitment and character you are pleased, then marry [your daughter or female relative under your care] to him." Undoubtedly your father's preventing you from marrying one who is suitable is something that is haraam. Marriage is more important than study, and it does not mean that you cannot study, because the two can be combined. What I advise my brothers who are the guardians of women to do, is to let them complete their studies; a woman may stipulate as a condition of her marriage that she be able to continue studying until her studies are complete.

Fataawa al-Mar'ah al-Muslimah, 2/704-705.

Secondly:

With regard to what you mention about the situation of the one who has proposed marriage and that he is still a student, being a student is not regarded as an impediment to marriage if he can afford to get married and to spend on his wife on a reasonable basis.

But if his being a student means that he cannot afford to get married and spend on his wife – apart from the unreasonable demands that some families make in the conditions that they stipulate – this is addressed by the words of Allaah (interpretation of the meaning):

"And let those who find not the financial means for marriage keep themselves chaste, until Allaah enriches them of His Bounty"

[al-Noor 24:33]

Al-Qurtubi (may Allaah have mercy on him) said: In this verse, Allaah commands everyone who is unable to get married and cannot find any means of doing so to keep himself chaste, because the most common obstacle to marriage is lack of money. So Allaah promises independence of means by His bounty, so that He will provide what one needs to get married or to find a woman who will accept a small mahr, or else remove from him the desire to marry." Tafseer al-Qurtubi, 12/242

It should be noted that the mahr and maintenance are the rights of the woman, not of her guardians. She has the right to agree to a little and to marry one whom she knows is poor, but it has to be pointed out that many woman may agree to marry a man even though he is poor when he proposes to her, then shortly after marriage the woman may start to complain, and that leads to arguments and divorce. This should be taken into consideration.

Thirdly:

We advise families and guardians not to be an obstacle to keeping their daughters and female relatives chaste because of the unreasonable conditions that they stipulate regarding spending on the basis that they want to be reassured about their daughters' future. This puts off the men who want to marry them, which leads to them being left on the shelf and the evils that result from that, especially nowadays when fitnah (temptation) is so widespread. Thus they harm themselves and their daughters when their intention is to do good.

We ask Allaah to set the affairs of the Muslims straight.

And Allaah knows best.