It depends on which Saamic language interests you.
I have a hunch that learning material for Northern Saami is fairly evenly divided between being published in Finnish on one side and Norwegian or Swedish on the other (for practical purposes, Norwegian and Swedish are close enough that if your reading knowledge of one of them is at a given level, your reading knowledge of the other is nearly as high. In other words, a Swede can use a textbook for a Saamic language that's published in Norwegian and vice-versa - listening comprehension will be trickier, though). One big advantage of teaching yourself enough Finnish to get access to learning material for Northern Saami is that many concepts in Saamic will already be familiar thanks to having seen it in Finnish (e.g. consonant gradation, vowel alternations, loanwords from Finnish, typological/structural similarities inherent in their being Uralic languages). On the downside, Finnish is likely unrelated or highly divergent from other languages that you already know. It'll take more time for you to get enough of a handle on Finnish compared to doing the same with Norwegian or Swedish given that you already know English.
One thing that I've noticed over the past couple of years of studying Northern Saami is that the amount of material online meant for speakers of English is slowly growing. Check out Giellatekno
and in particular the material at Oahpa!
. In the latter there's even a growing descriptive grammar
of Northern Saami in English which wasn't there when I started learning the language.
As to other Saamic languages, the tendency is that if you want to learn Southern Saami or Lule Saami, you're better off knowing Norwegian or Swedish (no surprise since native speakers of these languages live in Norway and Sweden) to take advantage of whatever learning material exists, while if you want to learn some Inari Saami or Kildin Saami, you're better off knowing some Finnish or Russian respectively.
Check out this thread
on HTLAL and scroll down to "Links" which contain links to learning material online in addition to schools and media (e.g. streamed TV shows).