Terminate w/o cause. Financial incentive for the tenant to move out?

[Raja Shan]

GM!
Have a one year lease with my tenant (which is their first year of tenancy) and want them to vacate as I've decided to sell my property. There is still 5 months to go but I want them to leave in spring (April) so I can put my place for sale.

Questions-

1) Willing to offer a financial incentive for them to leave.  I'm thinking of $1500/ (property rented for $2800/). Is this too much or reasonable? 

2) If they decide to take the offer and move out in April, does that override the 90 day notice needed (see below)?

Thanks for all the help!

Senate bill 608 for reference

If the specified ending date of the fixed term is within the first year of occupancy, landlord may terminate without
cause by giving the tenant 30 days’ notice prior to the specified ending date for the fixed term, or 30 days prior
to the date designated in the notice, whichever is later (90 days in Portland and Milwaukie).