Depending on how you're planning to go about making it and your own skill level when it comes to crafting the price can change up or down quite a lot. In this example thing I'm just going to assume you want to make a deer costume.
For example, here are three different prices for simply a headbase (Please note that all numbers aren't 100% correct but they should be close, and that shipping would most likely have to be included in some cases as well unless you go buy stuff in person):
~$125 if buying and hinged head if buying a ready-made unfurred resin base from for DVC.
~$70-80 if commissioning a head base from from someone else.
~$12-20 1 yard of half-inch thickness foam to form the head yourself.
According to some site, the average-ish amount of fur needed for a fullsuit is ~4-5 yards or 2-3 for a partial. In most cases it's probably best to have too much fur than too little, especially if it' going to be a digitigrade fullsuit.
Most furs seem to go for about $25/yard on fursuitsupplies, so multiplied it'd be about ~$50-125 for the furs excluding shipping.
Then there are the things like eyes and what style you want them in. Toony eyes are usually made from buckram, while some want the more realistic resin ones.
Costs for the buckram would be ~$1,50 (which you're going to need no matter what style you want I think since it's what people use to cover the tear-ducts in suits with resin eyes) and resin blanks are around ~$5. .
If you want hooves for the feet they seem to go for around $50 on DVC's Etsy page. I suppose those can be made yourself as well but I'm not too sure out of what and/or how.
For antlers some use actual real antlers while others make them from sculpey or resin.
I'm not too much of a crafter so I can't really say much about this particular step.
Jawsets and a tounge might be a bit tricky to find for a deer-suit, so you'd most likely have to make that yourself. Sculpey should work for that as well, and a tongue could be made out of felt.
If we now take the most expensive outcome possible from my calculation we should land at about $310 or so. I've probably missed a few steps and/or details here and there since I've never tried building a suit myself. Of course that sum is for picking the "easiest" and most expensive options in all cases mentioned above. It could be a lot less if you're good enough at crafts to make the headbase out of foam yourself and/or if you're only wanting to make a partial, for example. The fur is most likely going to be the most expensive thing no matter what.
This thread over here have some nice examples and posts made by people who (unlike me) actually know what they're talking about xP
https://forums.furaffinity.net/threads/29207-How-much-did-your-fursuit-cost-to-makeHopefully this helped a little at least and good luck with your project ^^'