If I were at your stage I might look at the Rossa* putter L55 (725 cr.) and glance at the cheapest (?) 3.5 meter ball:
Callaway HEX Chrome+ Balls (Slow Meter) (L1+)
2 spn 2 dis 3.5 meter 300 credits (3 balls)
But there are many other views and choices you may consider.
Or a 2.5 meter cheap ball like:
WGT GI3 S Vapor Pink balls @104 cr. a sleeve OR 99 cr. in white
*
Rossa putter
http://www.wgt.com/proshop/golf-clubs/putters/taylormade-daytona_putter_2011_l55.aspx?i=f00c3311-5877-4a8b-8f1e-d781f9f14281