Let's look at this with realistic expectations and some math. Or skip to the bottom for the results
Well, I get anywhere from 5-10 plat/hr depending on if my auctions sell, if I get attacked by other players, if invasions happen, if I get disconnected/stuck, the game crashes or is updated, etc etc etc. Considering the gold farming websites charge $10/100 plat, they wont pay that to farmers. They'll likely pay out $6 or so. so if you figure an average of 5p/hr (factoring in patches, disconnects, and all that) you're looking at 120 plat/day on average. Of course if it's just a botting account it's likely not geared very well and farms slower, so let's be conservative here and say 100 plat/day as an average.
That comes to about $6/day or $0.25/hr.
I would estimate my computer uses 300watts and electricity is cheap in my town (.17/kWh) so at 0.3kWh I'm looking at 5.1cents/hr in electricity. This means we get $0.209 in profit per hour, which comes out to $5.02/day in profits, or $150.60 per month. Subtract the $15/mo fees of rift, then the cost of owning the bot (47.99 euros = 67.7331 US dollars for 3 bots per year, comes to $1.88/mo/bot) brings your monthly profits to $133.80 (or $130 if you only use 1 bot). This is assuming you never get banned and can always find a site paying for plat.
TL;DR:
If you can run 3 bots at once 24/7 to use up the whole subscription then you'd be looking at about $400 a month in profits total, minus the initial costs of the games (+$70 if you run them all on one machine instead of 3 due to electric costs).
If you just run one bot 24/7 you'd be looking at about $130 in profits per month.
Wow, I sure do get bored at work.