Hi, the autocomplete list content, from where is provided? (Plain text, excel table, database, in memory, xml, web source..)
If it is not on plain text, xml or in code/memory, it would cost a few hours more, maybe 20usd plus.
I can make a library with a new frontend control to extend the textarea control for wpf and or a textbox for winforms.
If you only wish to have the textbox for winforms, the prices descend 20usd.
The control can be configured to only suggest or autocomplete.