Go to Centerline's website, in the Tech bulletins they have a real fine "economy" rebuild strategy.
Synchro rings and Synchro sleeves can be expensive and some are aftermarket that don't have a good reputation...Buy a used trans and use it for rebuild parts...
A proper trans rebuild done by "others" with removal and reinstall will easily run 2K$. You will find that clutch work seals etc makes sense to do at the same time...this will add $ to the job. So budget accordingly.
You may want to include the cost of a few quarts of transmission grease in that super budget rebuild.
Beyond that, one syncro ring and a pair of stong circlip pliers will be necessary. The fifth gear syncro sleeve can be turned around and used on the first/second gear and the firat/second sleeve put in fifths place - best side to the gear.
Check out other post here on the bb. There is a lot of intelligence recorded on the subject of transmission rebuilds.
The other way to go is to get the transmission in and out yourself and ship it to someone who can build you the transmission you want to be shifting for the next decade. I had mine rebuilt by Merritt Carden with lightened gears three years ago. He charged $700 at the time. For a mechnical incompetent like me it was money well spent, but I would bet even for those with some real rebuilding cred it would be hard to end up with a car that is as much of a pleasure to drive as one with one of his trannys.
Contact Alfar7, Richard Jemison. He is in Pensacola, Your rebuild cost depends on what parts need to be replaced, plus whatever per hour your specialist will charge. Richard does a lot of Alfa gear work, has the knowledge and experience to do a good job.
From my experience.
little italian,,, just made it better, never a second gear grind, and i can shift into fist gear so, so easy..and as for a rebiuld price, no part is over 35.00, gear, bearing, synco rings.. a full rebuild kit, all gaskets, bearings,and all the sycno's.. $95.00-125.00..and to boot , a ;ighter 1 peicer driveshaft.. no guibo, to worry about..