Try this

[VBA] statusLine = statusLine & "; Average=" & Format(.Average(Target), "##,##0.00")
[/VBA]

and various other formats (VBA taken from excel help page)

Format Function Example@import url(office.css);MyTime and MyDate are displayed in the development environment using current system short time setting and short date setting.
Dim MyTime, MyDate, MyStr MyTime = #17:04:23# MyDate = #January 27, 1993# ' Returns current system time in the system-defined long time format. MyStr = Format(Time, "Long Time") ' Returns current system date in the system-defined long date format. MyStr = Format(Date, "Long Date") MyStr = Format(MyTime, "h:m:s") ' Returns "17:4:23". MyStr = Format(MyTime, "hh:mm:ss AMPM") ' Returns "05:04:23 PM". MyStr = Format(MyDate, "dddd, mmm d yyyy") ' Returns "Wednesday, ' Jan 27 1993". ' If format is not supplied, a string is returned. MyStr = Format(23) ' Returns "23". ' User-defined formats. MyStr = Format(5459.4, "##,##0.00") ' Returns "5,459.40". MyStr = Format(334.9, "###0.00") ' Returns "334.90". MyStr = Format(5, "0.00%") ' Returns "500.00%". MyStr = Format("HELLO", "<") ' Returns "hello". MyStr = Format("This is it", ">") ' Returns "THIS IS IT".