Hi, and welcome to the hobby and the forum!
I am also retired, and of limited income, and building a dream Fiero...a yellow 88 CJB Formula with a Series II GTP L67. I have built a few muscle cars over the years, and this will probably be the last one. I am working out of a single bay garage, with an attached storage shed, and only during 3 seasons...so challenges are evident.
In my favor, I have plenty of free time, an understanding and very helpful wife, and a neighborhood that does not frown on shade tree mechanic work (more rare every day).
If you plan the outcome of your project with detail, you can form a parts list that maximizes your budget. Once that is done, leverage time and patience to accomplish the purchases, by waiting and watching for each part to become available at a reasonable price. I have almost everything needed to accomplish this build now, thanks to many members of this forum who have posted parts in the mall that fit my list...and others who posted on Craigslist and eBay.
Also, use the forum to sell any 'surplus' parts resulting from your work. The doodad collecting dust in the corner might be just what someone like me is waiting to see for sale. The income is useful to purchase miscellaneous small parts 'over the counter' for your own build. Good luck, have fun and keep us posted.
1988 Pontiac Fiero Formula, Yellow, original. (CJB #118)
1977 Pontiac Le Mans Can-Am W72, original, unrestored.
1977 Pontiac Grand LeMans
2003 Pontiac Grand Prix GTP L67/MN7 (Parts Car)
2001 Pontiac Grand Prix GTP L67/MN7 (DD)