First, there is cheaper parking available at San Ysidro for less than you paid.
Second, you can use a Park & Ride station (E Street, H Street, etc.) and trolley to the border.
Third, I'm not sure you'd save any significant money taking a taxi from Otay to someplace like La Mansion. Plus it could actually cost you more if your Spanish and taxi negotiating skills aren't up to snuff.
You could use a route taxi. But locals I know who live in Otay seldom go to El Centro because it takes too long.
There are "love motels" near the Otay crossing that some hobbyists use. El Ensueno is probably the most popular, but none are walking distance to the crossing so you'll still have cab fees to pay.
Some agencies will send escorts to Otay and others won't so check with the agency before making plans. Unless I was near Otay and just want a quickie I wouldn't see a chica in Otay.
As to saving time crossing the border:
Get a SENTRI Pass and you'll solve all your problems.
If you can't get a SENTRI then get a Passport Book/Card and use the Ready Lane.
Sometimes Otay lines also are very long. Crossing at Otay usually, but not always, save some time. But a SENTRI saves a lot more time.
The new crossing point--San Ysidro West--has (as of this posting) short lines. I've seen the line at San Ysidro west be 15 minutes when it is 1.5 hours at San Ysidro East.)
-- Modified on 10/3/2016 1:09:16 AM