It seems today's most popular actions are the MRC (Montana Rifle Company) and CZ.

The MRC is a M-70 style that handles up to .458 Lott and the CZ is a Mauser derivitive that can handle up to the .416 Rigby. Prices are under $500 for each.

The MRC I have right now is a very nice action for the money, however a trifle heavy, which is fine for the heavy recoiling arms. The CZ is on order and so I haven't seen it yet.