$99.75 in expenses (not counting time spent getting sales or building website)
5 total sales resulting in $450 of sales
108 hours of work done by you. We don't know how much time it took your brother to create the podcasts. Let's assume he didn't do the 6 podcasts perfectly in the first go.
30 days of total case study.
$350 in "profit"
Divide your profit by the hours you worked on it. $350/108 = $3.24 per hour.
Now let's consider setting up the website was a one time cost so moving forward your operating expense is $30/month to host the website and the podcasts[edit]
Let's take the hours your took to get the sales and divide those by the number of sales you got. 90/5 that comes to 18 hours per sale. Your average sale value was $450/5 = $90. Let's say your put a bare minimum hourly rate for your time of $10/hour that's $180 spent getting a $90 sale.
Now unless you get more visibility and are super savvy in promoting your podcast your ROI just doesn't pan out.
Let's see what your $1000 budget gets you in 3 months. Might be a good post to regenerate interest in your podcast. :)