Yeah well, entrance would be wasting only a couple of seconds, its bad, but affordable, for the garnet if you meant like... before the bat relic in one of those vases, thats more like half a minute to afford, and im not exagerating since youll fight a boss and lib card to come back, the third option outerwall is ... sort of moot since it would mean to waste nearly 2 minutes to get to library.
The low value of the zircoon could be a problem if the selling time exceed say... well 30 seconds, then the garnet would be better, yet its still the same issue; I dont know exactly how many $$ will be required.
For the prologue.... theres glitches involved, the most important one been the damage increase with holy water, theres no "exact" timing to cast your spell but tossing a bottle after will increase damage, youll have to figure timing, as they change depending your or drac position and cast time, AFAIK you can still whore a dozen of frames further than me.
Pro tip: to change drac position at start as well as where he jump, its all predetermined by candles you destroy before entering the room, im using the best outcome IIRC in any% but if you have different goals for the prologue you may adjust to something different.
The best timing I know off is in the old pcsx movie
[1363] PSX Castlevania: Symphony of the Night by arukAdo & pirate_sephiroth in 19:01.63, probly a few frames faster than current any%