Hi jack in my experience fitting an internal mic is its usually fraught with problems,feedback direction placement ,the best most useable results i've had is with external clip on condensers.
I have shure and microvox systems clip on and swan neck both work very well i have experimented with mounting them inside on everything from banjos to my club2 blending the mix with say a 20% inside 80% it can give a warmth but its very dependant on the amplification.
I have a AER compact 60 had them for years absolutely great amps and will amplify just about acoustic really well with very natural sound and dont feedback at the drop of a hat
I don't think theres a budget shortcut to amplifying acoustic instruments, i've certainly never found it
And as for the just bung an sm57 in it brigade as is the general suggestion ,don't get me started lol
I would suggest quality condenser mics and a quality amp ,your sound is only as good as its weakest link