I cant remember what it was when I was there a few months ago but I want to say it was $35 per person each way. So we called off going to universal because I wasn't about to pay $140 for 2 of us JUST to get there and back
The cheapest way to go, usually, is to rent a car. Sometimes a one-day rental can be had for less than $30, sometimes even $20. You add $15 for parking and $8-12 for gas, and it's a pretty decent deal at $43-57 round trip, and has a lot of flexibility.
If you don't want to drive, it gets trickier. By cab Sea World is about a $60-80 round trip. Universal is $90-110 round trip. That can go up because the cab is metered. If you sit in traffic, for example, the meter stays running. If you're going before 7 AM or after 9 AM, that's probably not a huge issue. On the way back, you want to avoid the 4-6PM range, but that's not usually an issue; most people leave Universal/Sea World much later.
The Mears shared van service from WDW to SeaWorld or Universal is $19 per person each way, so that's $76 for the two of you, plus tip. The van will pick up several people, so it's not quick. A cab is probably a better deal, certainly to Sea World, since it's taking just you and will drive direct. Traffic, again, can drive up the cab rate.
Limo is about $80 round trip to Sea World, $100 to Universal, plus tip.
There is a local bus, route 50, that goes from WDW to Sea World. It's sloooow, like 50 minutes or more, but super cheap. It picks up at the TTC, so you also need to figure in the time to get to the TTC.