The first startup I worked for had 1 IT guy among 12 people, and everything was in-house, including servers. The second grew to 50 people and did not ever employ an IT guy for internal work - most stuff was run on SaaS and the total cost was less than an IT guy salary. Any admin was done by taking engineering time, and no-one wanted to divert that away from product to do in-house stuff. Because when you're taking time away from product, it's not just the salary but the opportunity cost, because any investment in product is supposed to return a multiple.