It all depends on the amount of features you need in the new community, the platform you are already using and the amount of data you want to migrate. Explain your requirements for getting a better quote.

We have already done migrations from Ning, Joomla community builder, Dolphin, phpfox to Elgg.

I agree with RPGRealms. I'd start with these plugins:

likes
elgg-crypt
mood
wp1
quotes
elggzone_darkgrey

They are all third party plugins that I'm not familiar with. If you do find the plugin that causes this, please report back. It could be the plugin is exposing a problem in Elgg or the plugin could have a bug.

I found the conflict it is the mod  seems no one has been able to come up with a fix

http://community.elgg.org/pg/plugins/bman/read/504003/customstyle-11-elgg-17

Thanks

Lexxie

Yup, ran into the same error here with that plugin. Was going to mention that one but didn't see it in your list.