It is a common practice in writing Sanskrit to exchange व abd ब both are correct in writing. I don't know how Valmiki did pronounce or Sugriva called the name. But here is Monier Williams attesting both the words in use:
वालिन्
(H2) वालिन् [p= 946,2] [L=192145] m. (also written बालिन्) " haired or tailed " , N. of a दैत्य MBh.
It is the name of a demon also. Also the name of a monkey you have referred to in Ramayana:
of a monkey (son of इन्द्र and elder brother of the monkey-king सु-ग्रीव , during whose absence from किष्किन्ध वालिन् usurped the throne , but when सु-ग्रीव returned he escaped to ऋष्यमूक) MBh. R. &c used both in Mahabharata and Ramayana.
Now you can judge yourself whichever is correct according to you. But Sanskrit accepts the interchange of the letter va with ba. VS Apte has got a different meaning for बाली --
बाली bālī
बाली A kind of ear-ring.
Also
बालिन् bālin : (page 1163)
बालाकिः bālākiḥबालाकिः N. of an ancient sage; दृप्तबालाकिर्हानूचानो गार्ग्य आस Bṛi. Up.
बालिन् bālinबालिन् m. N. of a monkey; see वालि.
बालिनी bālinīबालिनी The constellation Aśvini.
बालिः bāliḥबालिः N. of a celebrated monkey-king; see वालि.
It is इकाराब्त and also इन्नन्त declined as दण्डिन्।