There are Pros and Cons for both the approaches . Build vs Buy is always a decision that requires considerable moderation

I am assuming that you are just starting your business , so with this assumption the following pointers may help
a) what is the value add you bring with your job board
b) what is the differential your job board will bring as compared to other job boards in the market

So you have to weigh in against the following
for Buy / reuse : no maintenance, can avail support , to some extent less effort and hence less cost
but then you will have a generic job board , duplicate of other job boards
For Build : Specific to your values,unique to represent your differential
cons: maintenance, support, cost and may be time to market

we can discuss this in detail if you like