1990 toyota 4runner automatic transmission trouble?

i have a 1990 Toyota 4runner with 260,000 miles, 4 doors, 4wd with an auto transmission. the problem I'm having is after it warms up the transmission likes to stick in drive and i have to manually using the shift lever put it into first, and many times i cant even put it into second gear manually, it will skip straight to drive even with the shifter in second.it doesn't seem to be burning fluid. I've been told that it the shift actuator, if so any ideas on cost of the repair ? i personally was hoping a filter and fluid change would fix it thinking that the old fluid may be gumming up the springs.