The current price for those dates shows about $280 round trip on United with one stop. That averages $140 for each direction. I'm not an expert on that route, but I do price transcontinental flights between South Florida and Southern California. For those, if I get something under $150 one-way, I feel like I'm got a good rate. Of course, every route is different, so you need to check it (more on that later).
If you must fly nonstop, you only have a few options. Those price out at $366 or $386. Personally, I'd take a one-stop itinerary to save $86 per person. But, other folks may feel differently.
I've found that the best way to determine the "normal" price for a discounted airfare is to check the same routes on surrounding dates. For US domestic flights, you almost never see fares that require a round-trip to save money. As such, searching for one-way fares is the best method.
I use the ITA Software Matrix. ITA is the company that powers Google Flight searches. (Google bought them years ago because they had the best product for retail airfare.) The ITA Matrix only shows fares. You have to go elsewhere to buy them. But, it's great for research.
http://matrix.itasoftware.com/
Here's current (as of January 7, 2019) one-way fares between San Francisco (SFO) and Orlando (MCO) for June 2019:
And the return, in July 2019:
What these calendars tell me is that the cheapest fares from SFO to MCO would be about $110 or $120. And, a reasonable bargain would be somewhere around $150.
For the return, the best rates are also $110. Based on the multiple times that figure appears, the demand from Orlando appears to be less than the demand to Orlando. Similarly, if you're not flexible with your travel date, getting a fare for $150-160 would still be a reasonable deal.
As
zoo2tycoon notes, there's a bit of guess work involved. Something major could happen and prices could drop or rise substantially. But, absent a major event that affects the economy (terrorism, airline bankruptcy, etc), I'd use $110 as a great deal and $150 as a reasonable deal for each one-way fare.
Personally, if the current one-stop flights on United work for the schedule, I'd book and not look back. If I had any flexibility with dates (particularly if I was booking multiple tickets), I'd look into departing a day early. Doing that brings the fare down to $226. And one of the options at that fare involves an overnight flight, which means you're still arriving in Orlando on June 19.
I hope some of that helps. Feel free to ask follow-up questions.
Added: I also priced Southwest for those dates. Their lowest fares are $220 in each direction ($448 round trip).