Without hesitation , it would be the excellent GSO ( Guan Sheng ) 'Superviews' from Andrews communinations , the 15mm and 20mm are only $39 each and these with a good GSO 2x Barlow at $29 will give you a good spread of magnifications 95x with the barlowed 15mm , 70x with the barlowed 20mm , 46x with the 15mm on its own , 35x with the 20mm on its own and then 28x with your own 25mm .
All for $107 but if this is to much start with getting the 15mm and I guarantee it will become the most used eyepiece you own , these are that good then save up for the 20mm then Barlow , these are excellent eyepieces rivalling my $300+ TelVue Panoptics , awesome eyepieces that will make your scope perform as good as it can and that's very well on the moon , planets and double stars etc.
Brian.