Sub 25K, I'm afraid you probably won't find much (but see below).
The old saying:
If you can't afford a new Porsche, you can't afford an old one!
This is not ment to be flippant. The late 60's-early 70's models cost MORE to refurbish than the more recent models ('80's-90's).
I've got a '91 911 C4 that I bought over from the UK and it costs peanuts to run compared to say, a '72 911E / S.
The 1970's Porkers are lovely, light and frisky, but they're also unreliable rust-buckets with fit and finish only just above that of a 60's Skoda.
An indicator will likely set you back 3-400 squids.
Badges aside - if I wanted a sports car to actually
sport around in, its very difficult, IMO, to go past a well-sorted, old-style Toyota MR2.
Apart from A Vauxhaul (Holden) VX220, of all the cars I've driven (Lots!!!)
the MR2 was the most out-and-out fun. Quick. Good power to weight and a rock-solid engine. Excellent handling, easy to drive - hits all the boxes.
Also:
A well-sorted mid-late '70's Alfa convertible. Not as expensive to run as a contemporary Porsche and arguably better looking.
Of the 'awesome' vintage cars I've driven:
Bentley Speed Six: More victories than the 4.5 supercharged. Six-seven figures. Need a B-Double license.
Jag XK 140 DHC: A monster-well fun in that "I don't care if I die" mold.
Handled like a bus.
Jag C-Type: Just...well.... just! Too much noise, too much power, no brakes - as above but more so! No comforts. Orgasmic.
Ferrari 246 GTS: The Toyota MR2+++ of its day
!
Ferrari Daytona: Sell Mummy.
Ferrari F360: Sell Mummy AND Sis.
Ferrari 275 GTB 4 cam. Sell everyone!
Dodge Super Bee w/396 Hemi: 0-60 time only bettered in the last 5 years (3.91 timed at Portland IR). I owned one of these. I paid $2700 for it at the height of the oil embargo. Easy 150-200K now. Sob!
Lambourghini Diablo: No.
Lanbourghini Murciellego. Yes.
McLaren: No. Absolutely not. Silly, Silly Silly car. You will die. With a smile on your face!!!
Lotus Europa TC: If you can find one that stays together - grab it!
Lotus Elise: Involving. Depreciating. Glued together chassis not for Aussie roads.
Porsche 928: Again; well sorted, its probably the best GT car ever. (Pretty cheap too!)
MG 'F': Hmmmnnn. A bit tweedy.
MGA MKiii: Oh yes. That's it baby - right there! Very sexy little car. Quick (ish) and curiously reliable.
Honda NSX: Best Supercar in the world. 290kph with no fuss.
Austin Healey 3000 MKi: Hmmmmnnnn. Also tweedy.
Audi TT: "How would Sir like it cut this week?"
And finally:
1991 Porsche 911 C4 Woooo - hoooooo!!!
With modded suspension, EMS, exhaust and gearing ( 50-110 in 4.41)
AC is stuffed. Its covered in mud & grass. A frog lives up front and a has ding in the side door where a cow sat on it. Who cares!!!!
Getting your perfect car is like getting your perfect telescope. It'll probably never happen, but the thrill is in the chase!
G'Luck.
Peter
(PS: I assume you meant someone else!)