You really need to take it apart to inspect it for damage, scoring on the camshafts, tappets likely to need replacing, cam chain tensioner and probably the turbo (assuming you its a turbo engine you have as you failed to mention what engine it is) normally you would get away without damage done to the big end bearings and crankshaft, if it wasn't driven for long or hard with slightly low oil.
In terms of price, a set of tappets, assuming once again you have a 20vt engine cost me upwards of £400 for the part from VW this was a few months ago. For the cams you should be able to source a good condition second hand set relatively cheap. If you have a 20vt the cam chain tensioner and chain is likely to need replacing, price varies from non-vvt to vvt unit, but expect to pay upwards of £60 for a second hand vvt unit.
