Ur wife is supposed to be your partner.

Some tips:
1. Talk to wife, tell her how much u likely willing to fork out for dowry. Then get her to also find out likely how much her mom is thinking of. Most importantly, can your wife find out whether her mom may pass the money back to her anyway (some moms don't keep the money, they just want to get more money so that they can pass to daughter)
2. How tables are you giving them? (The ang pow for those tables they will collect their own). If you give them 10 tables, ur dowry can be ramge from 8888 onwards depending on how much u want to give. If it's 15-20 tables, then range from 5888 onwards.
3. If during negotiation stage when u meet in-laws and you propose the sum, and they reject. Ask them how much are they thinking of. If it is over budget, tell them you get back to them as u need to try find the money.
4. Causally mention you need to set aside some money savings for after wedding. But if they are insistent to the extent where it is on the verge of quarrel. Tell them you will get back to them.

Frankly, to be blunt, a middle income family usually will not ask for over the top amount. As it will look like they are selling their daughter. Typically, I seen poorer families asking for more dowry, statistics wise. (Not because they are money hungry).
If your wife side her mom, normal. She is on both fences. Not easy to manage. But if she scolds you and treat you like ATM, then best is you find another girl. Plenty of fishes.

If I am you, if I won't marry the girl if she is not siding me. It's not about the amount or church. It's the thoughts that count. You be unhappy about the relationship.

By the way, for her asking for church wedding. That's quite Okie. No fault of hers.