Im in the process of changing my VT Calais shocks as well. Just changed my rears tonight, the monroe's i took out were rooted. I could push them in and out with no effort what so ever.
Replacing front + Rear with KYB Excel-G. Made a huge diff in the rear when i took it for a test drive just before. But then i guess i actually have shocks again not just useless metal.
For a lowered car:
Front Struts = $250 for pair
Rear Shocks = $98 for pair.
Thats from Tubular Suspension systems posted out for $28 with a heap of other stuff.
I had Koni Adjustables in my last car they are a nice choice too but aren't cheap