Depends on the jobs you want to do – and more importantly the diameter of the holes you want to drill.
– for 3mm steel – not too much problem – unless the diameter is large.
– Fence post – more things to think about :
Use an Auger bit if you need a deep clean hole – spade is messier – Forstner is often too short.
Pillar drill – old classic ones are great if:
You can get one that is not worn out/broken
You can lift them – my Meddings is over 100kg needs 2 strong folks to move.
You have somewhere to put it – very strong bench/stand
You are prepared to wait find one
New Drills :
Easily available – huge choice and price range
They generally do the job – some have run out or play but actually this
is not a big problem unless you are expecting milling machine accuracy,
decent drill bits and appropriate work clamping/positioning are more important.
Probably the biggest consideration should be what you expect to doing to the fence posts – you will need an expensive/new big/old pillar drill to drill right through the posts.
-typical stroke of modern pillar drill 80-100mm
-my old/big Meddings – 127mm .
You could start the fence posts off in a smaller pillar drill with an Auger bit and finish with hand held drill. This is what I did recently needing to
do an accurate job “on-site” – I used a small morticer (similar to pillar drill )that I could easily lug about and use on the floor with the fence post .