I would think that either Chevron Supreme (1.08 approx.) or Mobil Drive Clean (1.17 approx.) would be great. Pennzoil would also do an excellent job--here in KY it is 1.63 per quart and is a fine group 2+ oil in my opinion.
I have been using Quaker State 10W30 for
my Miata 95M. Now milage is up to 70K.
No problem at all. Now I am considering
using Pro-line from Pepboys $1.09/qt,
I hear it is the same staff as Quaker State.
The cost for my oil change is
3.5qt x $1.09/qt = $4
plus I get super-tech filter from Walmart
The total cost is less than $7.00.
I change my oil every 2000 to 3000 miles, never
over 3000 miles.
Castrol GTX is another good choice as it has a bit of moly in it. If you only drive the car in the warmer weather you might want to try Pennzoil 15w40 as it has a good 150ppm of moly in it (the SJ version did anyways, hopefully the SL is the same!)
Havoline from Chevron/Texaco (not the Equilon) has the same specs as the Chevron Supreme and is sold at my local Target for $.94 a quart. That and Pennzoil in the 5 qt jug for $7 at Wal-Mart are my choices for bang for the buck oil.
Patman may have a point with the Pennzoil 15w40. Although it is a "diesel" oil, it is labled as a "long life" oil, so it may have more detergents and better TBN retention so you may be able to slightly extend your drain interval. It is $6 a gallon.