Building a biller can be done in house by one of your Devs who will treat it as an avoid at all costs 4 day old dog turd on a sidewalk. However, most Devs consider being labeled Billing Bitch worse than a bad burrito lunch. Thus, given your Devs will consider this the most thankless impossible to please and deliver on time headache no one will step up thus delaying your payment systems launch and costing you money, your likely better off just getting one from a reputable provider. Here are some good options if your Devs are way too lazy and underpaid to motivate themselves to step up to the challenge of coding your own internal billing system or you don't want to take the chance that the new guy with the pencil mustache on the student work term can figure it out over the summer;
3. Aria Systems
However, if you are able to find a Dev with payment system and biller design and coding expertise and the willingness and motivation to lead and manage you payment projects and team - HIRE AT ALL COSTS!