Im using a system like that too. but using the psionic rules in 3.5 as my guide. Spontanius casters are still spontanius and prepare casters still prepare.
Sampel spell point cost
Prepaerd catser
1stlv 1sp 2nd lv 3sp 3rd lv 5sp ext.
spontanous caster
1stlv 1sp 2nd lv 4sp 3rd lv 6sp ext
it costs 1 point more per caster level for spontaious casters but thay get 1 point more for each of thear spells above 1st.
basikly take the number of spells that thay can cast of a given spell level and multiply it by the level that thay can 1st cant that level spell spell. repeat for all levels get u your spell points. a caster can not use more spell points in a spell than caster level