My Monk: http://us.battle.net/d3/en/profile/Sowtis-1686/hero/5480474

What items should I start replacing? When do I want to get rid of Inna's?

I know I can get better weapons, Echoing Fury could have some base CD with the socket and Won Khim Lau could use some more damage overall but those will be rather expensive.

Anything I could upgrade that won't cost more than 100m per item? Or is that what I have to do now, save up a pile of cash and blow it on one item? xD

Can add vit, single res, or avg dmg on ammy

Vit on innas pants

Belt you can either go with 125+ dex/vit/Single res/AR for pretty cheap and get a vit/dps/res boost, or obviously Witching Hour for the pure DPS boost.

Your crit dmg is a bit low. If you'd be willing to lose the LoH and Elite % on unity, look for the basics. Dex/Single res/CC/CD, base dmg and vit if you can.

Armor and ring gems could be up'd of course.

These are all relatively small upgrades DPS wise, but boosting your vit/res while keeping current DPS would be a significant upgrade in itself.

upgrade gems, witching hour instead of inna belt, won khim got really low dps try to find some rare weapons they are not very expansive if u snipe the right one.
i think that these are the cheapest improvements that you can do with low budget.

Your Ehp is 300K .. too low.
Armour .... 4859 (little higher)
Life ........ 33K (try for 45K)
All res ..... 457 (try for 600-650)

You have 4 piece innas. TR ?
Can you do with 2 innas (Helm & Pants) ?

The real question is ... your gears pretty much max out at about 100K dmg
If you wanna be 150 - 200K .... you gonna need all new gear and pricey.

Have a look at my gear.